TWI840757B - Compositions containing cellulose nanofibers - Google Patents

Abstract

One aspect of the present invention provides a rubber composition in which cellulose nanofibers are well dispersed in rubber and can form a molded body with excellent elastic modulus, wear resistance, etc. One aspect of the present invention provides a rubber composition, which includes: cellulose nanofibers, a first rubber component as a liquid rubber, and a surfactant. In one aspect, the cellulose nanofibers do not have an ionic group. In another aspect, the number average molecular weight of the liquid rubber is 1,000 to 80,000.

Description

Compositions containing cellulose nanofibers

One aspect of the present invention relates to a composition comprising cellulose nanofibers.

In the past, rubber molded products were required to have a high balance of various properties such as mechanical strength, flexibility, wear resistance, and processability. For example, fillers were usually included in rubber molded products to improve elastic modulus, hardness, and wear resistance. In order for such filler-containing rubber molded products to exhibit the required properties, it is important that the fillers are well dispersed in the rubber.

For example, Patent Document 1 describes a rubber composition for tires, which is characterized in that oxidized cellulose nanofibers are blended into diene rubber including modified diene rubber to improve mechanical properties. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2019-147877

[The problem the invention is trying to solve]

As awareness of environmental issues has been increasing in recent years, various attempts have been made to use cellulose, a low-density and renewable material, as a filler in rubber moldings. Among them, cellulose nanofibers have great potential as fillers for polymer moldings because they provide a good reinforcement effect per unit usage of the polymer molding when combined with various polymers to form the polymer molding. If such cellulose nanofibers can be used in rubber moldings, it is possible to provide rubber moldings that can be used for a variety of purposes due to their low specific gravity and excellent physical properties, and are also more advantageous in terms of transportation costs and disposal costs. However, cellulose nanofibers are essentially hydrophilic due to the action of hydroxyl groups in cellulose, and therefore are generally difficult to mix with rubber, which is a material with high hydrophobicity. Patent document 1 describes a tire rubber composition in which oxidized cellulose nanofibers as a filler are dispersed in a diene rubber including a modified diene rubber. However, this technology is a technology for improving the dispersibility by increasing the affinity of oxidized cellulose nanofibers for diene rubbers with modified diene rubbers. A rubber molded body in which cellulose nanofibers are well dispersed in rubber even if the cellulose nanofibers do not have ionic groups has not yet been provided.

One aspect of the present invention aims to solve the above-mentioned problem and provide a rubber composition in which cellulose nanofibers are well dispersed in rubber and can form a molded body with excellent elastic modulus, wear resistance, etc. [Technical means for solving the problem]

The present invention includes the following aspects. [1] A rubber composition comprising: cellulose nanofibers, a first rubber component as a liquid rubber, and a surfactant. [2] The rubber composition as described in aspect 1 above, wherein the cellulose nanofibers do not have an ionic group. [3] The rubber composition as described in aspect 1 or 2 above, wherein the number average molecular weight of the liquid rubber is 1,000 to 80,000. [4] The rubber composition as described in any one of aspects 1 to 3 above, wherein the ratio (Mw/Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) of the liquid rubber is 1.5 to 5. [5] The rubber composition as described in any one of aspects 1 to 4 above, wherein the viscosity of the liquid rubber at 80°C is 1,000,000 mPa·s or less. [6] The rubber composition as described in any one of aspects 1 to 5 above, wherein the viscosity of the liquid rubber at 25°C is 1,000,000 mPa·s or less. [7] The rubber composition as described in any one of aspects 1 to 6 above, wherein the viscosity of the liquid rubber at 0°C is 1,000,000 mPa·s or less. [8] The rubber composition as described in any one of aspects 1 to 7 above, wherein the liquid rubber comprises one or more selected from the group consisting of diene rubber, silicone rubber, urethane rubber, polysulfide rubber and hydrogenated products thereof. [9] The rubber composition as described in any one of aspects 1 to 8 above, wherein the degree of substitution of the cellulose nanofiber is 0. [10] The rubber composition as described in any one of aspects 1 to 9 above, comprising 0.5% by mass to 10% by mass of the cellulose nanofiber. [11] The rubber composition as described in any one of aspects 1 to 10 above, comprising 10 parts by mass to 200 parts by mass of the surfactant relative to 100 parts by mass of the cellulose nanofiber. [12] The rubber composition as described in any one of Aspects 1 to 11 above, wherein the surfactant is a nonionic surfactant or a cationic surfactant. [13] The rubber composition as described in Aspect 12 above, wherein the surfactant is a nonionic surfactant. [14] The rubber composition as described in Aspect 13 above, wherein the nonionic surfactant is a compound having a hydrophilic group and a hydrocarbon group, and the hydrophilic group is selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfonic acid group, and an amino group. [15] The rubber composition according to aspect 13 or 14, wherein the nonionic surfactant is a compound selected from the group consisting of the following general formula (1): R-(OCH ₂ CH ₂ ) _m -OH (1) [wherein R represents a monovalent aliphatic group having 6 to 30 carbon atoms, and m is a natural number less than the number of carbon atoms of R]; and the following general formula (2): R ₁ OCH ₂ -(CHOH) ₄ -CH ₂ OR ₂ (2) [wherein R ₁ and R ₂ independently represent a hydrogen atom, an aliphatic group having 1 to 30 carbon atoms, -COR ₃ {wherein R ₃ represents an aliphatic group having 1 to 30 carbon atoms}, or -(CH ₂ CH ₂ O) _y -R ₄ {wherein R _[4] represents a hydrogen atom or an aliphatic group having 1 to 30 carbon atoms, and y is an integer from 1 to 30}]. [16] A rubber composition as described in any one of aspects 1 to 15 above, wherein at least a portion of the surface of the cellulose nanofiber is coated with the first rubber component. [17] A powder, which is composed of the rubber composition as described in any one of aspects 1 to 16 above. [18] The powder as described in aspect 17 above, which has a tap density of 0.01 g/cm ³ to 0.30 g/cm ^3. [19] A masterbatch, which is a mixture of the powder as described in aspect 17 or 18 above and the second rubber component. [20] A method for producing a masterbatch, comprising the steps of: kneading the powder as described in the above embodiment 17 or 18 with a second rubber component to obtain a masterbatch. [21] A rubber composite, which is a mixture of the powder as described in the above embodiment 17 or 18 or the masterbatch as described in the above embodiment 19 and a third rubber component. [22] The rubber composite as described in the above embodiment 21, wherein at least a portion of the surface of the cellulose nanofiber is coated by the first rubber component. [23] A method for producing a rubber composite, comprising the steps of: kneading the powder described in Aspect 17 or 18 above with a third rubber component, or forming a masterbatch using the method described in Aspect 20 above, and then kneading the masterbatch with a third rubber component, thereby obtaining a rubber composite. [24] A method as described in Aspect 23 above, wherein in the rubber composite, at least a portion of the surface of the cellulose nanofibers is coated by the first rubber component. [25] A rubber cured product, which is a cured product of the rubber composite described in Aspect 21 or 22 above. [26] A method for manufacturing a rubber hardened product, comprising: a step of obtaining a rubber composite by the method described in Aspect 23 or 24; and a step of hardening the rubber composite to obtain a rubber hardened product. [27] A shoe outsole, comprising a rubber hardened product as described in Aspect 25. [28] A tire, comprising a rubber hardened product as described in Aspect 25. [29] An anti-vibration rubber, comprising a rubber hardened product as described in Aspect 25. [30] A transmission belt, comprising a rubber hardened product as described in Aspect 25. [Effects of the Invention]

According to one aspect of the present invention, a rubber composition can be provided in which cellulose nanofibers are well dispersed in rubber and can form a molded body having excellent elastic modulus, wear resistance, etc.

Hereinafter, the exemplary embodiments of the present invention (hereinafter referred to as "the present embodiments") are described, but the present invention is not limited to such embodiments. Furthermore, the characteristic values of the present invention, unless otherwise specified, refer to the values measured by the method described in the [Embodiment] section of the present invention or the method understood by the industry to be equivalent thereto.

"Rubber composition" One aspect of the present invention provides a rubber composition comprising: cellulose nanofibers, a surfactant, and a first rubber component as a liquid rubber. Cellulose nanofibers are essentially hydrophilic due to their hydroxyl groups, while rubber is essentially hydrophobic, and it is usually difficult to evenly disperse cellulose nanofibers in rubber. For example, dispersibility can be improved to a certain extent by using a dispersant, but from the perspective of preventing the physical properties of the molded body from being reduced, it is more ideal to reduce the need for additives to a minimum while evenly dispersing cellulose nanofibers in the rubber. The inventors of the present invention have conducted various studies based on this viewpoint and have found that by dispersing cellulose nanofibers in a specific rubber having fluidity at a predetermined temperature to prepare a rubber composition, and then kneading the rubber composition in the form of, for example, a rubber masterbatch with a rubber to produce a rubber composite, a rubber cured product can be formed that does not impair the originally expected physical properties of the rubber and that well exhibits the reinforcing effect of the cellulose nanofibers. According to the rubber composition of the present embodiment, a rubber cured product can be formed in which cellulose nanofibers are well dispersed in the rubber and have good properties (especially elastic modulus, hardness, etc.), and such a rubber cured product can form a molded body in which cellulose nanofibers are well dispersed in the rubber and have excellent elastic modulus, wear resistance, etc. Below, suitable examples of each component of the rubber composition of the present embodiment are described.

<Cellulose nanofiber> As raw materials for cellulose nanofiber, natural cellulose and regenerated cellulose can be used. As natural cellulose, wood pulp obtained from wood species (broad-leaved trees or coniferous trees), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton lint, ramie, straw, etc.), cellulose aggregates produced by animals (such as ascidian), algae or microorganisms (such as acetic acid bacteria) can be used. As the regenerated cellulose, regenerated cellulose fibers (rubber, cuprammonium rayon, Tencel, etc.), cellulose derivative fibers, regenerated cellulose obtained by electrospinning or ultra-fine filaments of cellulose derivatives, etc. can be used.

In one embodiment, cellulose nanofibers are obtained by treating pulp or the like with hot water at 100°C or above, hydrolyzing hemicellulose to make it brittle, and then mechanically defibrillating it by a high-pressure homogenizer, a fine fluid homogenizer, a ball mill, a disk mill, a stirrer (e.g., a homogenizer) or the like to obtain fine cellulose fibers. In one embodiment, the number average fiber diameter of the cellulose nanofibers is from 1 nm to 1000 nm. The cellulose nanofibers may also be chemically modified as shown below, but in terms of the reinforcing effect as a filler, it is preferably not chemically modified. For example, cellulose nanofibers that are defiberized by chemical oxidation treatment using 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO) phosphate have a tendency to have lower heat resistance due to the ionic groups (such as carboxyl groups) introduced into the cellulose nanofibers, and the fiber diameter after defiberization tends to decrease. In terms of the reinforcing effect as a filler, cellulose nanofibers that are only mechanically defiberized (i.e., not subjected to chemical defiberization treatment such as oxidation) are more advantageous. Therefore, in a preferred embodiment, the cellulose nanofibers do not have ionic groups. Furthermore, in the present invention, the cellulose nanofibers having no ionic groups refer to the ionic group content measured by conductivity titration being less than 0.1 mmol/g.

The slurry can be prepared by dispersing cellulose fibers in a liquid medium. The dispersion can be carried out using a high-pressure homogenizer, a fine fluid homogenizer, a ball mill, a pan mill, a stirrer (e.g., a homogenizer), etc. For example, the above-mentioned defibration product can be obtained in the form of a product of the slurry preparation step of the present invention. In addition to water, the liquid medium in the slurry can further include any other liquid medium (e.g., an organic solvent) alone or in combination of two or more. As the organic solvent, commonly used water-miscible organic solvents can be used, for example: alcohols with a boiling point of 50°C to 170°C (e.g., methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, etc.); ethers (e.g., propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (e.g., formic acid, acetic acid, lactic acid, etc.); esters (e.g., ethyl acetate, vinyl acetate, etc.); ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.), etc. In a typical embodiment, the liquid medium in the slurry is substantially only water.

Cellulose raw materials contain alkali-soluble components and sulfuric acid-insoluble components (lignin, etc.), so alkali-soluble components and sulfuric acid-insoluble components can also be reduced through purification steps such as delignification based on cooking treatment and bleaching steps. On the other hand, purification steps such as delignification based on cooking treatment and bleaching steps will cut the molecular chain of cellulose, causing changes in the weight average molecular weight and number average molecular weight. Therefore, the purification step and bleaching step of the cellulose raw material are preferably to control the weight average molecular weight of the cellulose nanofiber and the ratio of the weight average molecular weight to the number average molecular weight to reach an appropriate range.

In addition, the purification steps such as delignification and bleaching based on the cooking process will reduce the molecular weight of cellulose molecules, so there is a concern that these steps will lead to low molecular weight of cellulose nanofibers; and cause the cellulose raw material to deteriorate and increase the presence ratio of alkali-soluble components. Alkali-soluble components have poor heat resistance, so the purification step and bleaching step of the cellulose raw material are preferably to control the amount of alkali-soluble components contained in the cellulose raw material to a range below a certain value.

In one embodiment, from the perspective of improving the physical properties of the cellulose nanofibers, the number average fiber diameter of the cellulose nanofibers is preferably 2 to 1000 nm. The number average fiber diameter of the cellulose nanofibers is more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 500 nm or less, or 450 nm or less, or 400 nm or less, or 350 nm or less, or 300 nm or less, or 250 nm or less.

From the viewpoint of improving the mechanical properties of the rubber composite containing cellulose nanofibers with a small amount of cellulose nanofibers, the average fiber length (L)/fiber diameter (D) of the cellulose nanofibers is preferably 30 or more, or 50 or more, or 80 or more, or 100 or more, or 120 or more, or 150 or more. The upper limit is not particularly limited, but from the viewpoint of operability, it is preferably 5000 or less.

In the present invention, the fiber length, fiber diameter, and L/D ratio of cellulose nanofibers are obtained as follows: using a high shear homogenizer (e.g., manufactured by Nippon Seiki Co., Ltd., trade name "Excel Automatic Homogenizer ED-7"), the aqueous dispersion of cellulose nanofibers is dispersed under the treatment conditions of a rotation speed of 15,000 rpm × 5 minutes to obtain an aqueous dispersion, the obtained aqueous dispersion is diluted to 0.1-0.5 mass % with pure water, cast onto mica and air-dried, and the air-dried product is used as a measurement sample, and measured using a scanning electron microscope (SEM) or an atomic force microscope (AFM), thereby obtaining the fiber length, fiber diameter, and L/D ratio of the above-mentioned cellulose nanofibers. Specifically, under an observation field with a magnification adjusted so that at least 100 cellulose nanofibers are observed, the length (L) and diameter (D) of 100 randomly selected cellulose nanofibers are measured, and the ratio (L/D) is calculated. For the cellulose nanofibers, the number average of the fiber length (L), the number average of the fiber diameter (D), and the number average of the ratio (L/D) are calculated.

Alternatively, the fiber length, fiber diameter, and L/D ratio of cellulose nanofibers contained in powders, rubber compositions, rubber masterbatches, rubber composites, etc. can be confirmed by using them as measurement samples and measuring them by the above-mentioned measurement method.

Alternatively, the fiber length, fiber diameter, and L/D ratio of cellulose nanofibers contained in powders, rubber compositions, rubber masterbatches, rubber composites, etc. can be confirmed by the following method: dissolving the polymer component contained therein in an organic or inorganic solvent that can dissolve the polymer component, separating the cellulose nanofibers, and fully washing them with the above-mentioned solvent, replacing the solvent with pure water to prepare an aqueous dispersion, diluting the cellulose nanofibers to a concentration of 0.1 to 0.5% by mass with pure water, casting them on mica, and air-drying them. The air-dried ones are used as measurement samples and measured by the above-mentioned measurement method. At this time, more than 100 cellulose nanofibers were randomly selected for measurement.

The crystallinity of cellulose nanofibers is preferably above 55%. If the crystallinity is within this range, the mechanical properties (strength, dimensional stability) of cellulose itself are higher, so when cellulose nanofibers are dispersed in rubber, the strength and dimensional stability of the rubber composite tend to be higher. The lower limit of the crystallinity is more preferably 60%, more preferably 70%, and most preferably 80%. There is no particular upper limit on the crystallinity of cellulose nanofibers, and the higher the better. From the perspective of production, the upper limit is preferably 99%.

Alkaline-soluble polysaccharides such as hemicellulose and acid-insoluble components such as lignin exist between microfibers and between microfiber bundles of plant-derived cellulose nanofibers. Hemicellulose is a polysaccharide composed of sugars such as mannan and xylan, which hydrogen bonds with cellulose to play a role in connecting microfibers. In addition, lignin is a compound with an aromatic ring, and it is known to covalently bond with hemicellulose in the cell wall of plants. If the amount of impurities such as lignin remaining in the cellulose nanofiber is large, it may discolor due to the heat during processing. Therefore, from the perspective of suppressing the discoloration of the rubber composite during extrusion and molding, the crystallinity of the cellulose nanofiber is preferably within the above range.

The so-called crystallinity here is obtained by the Segal method using the following formula based on the diffraction pattern (2θ/deg. is 10-30) when the sample is measured by wide-angle X-ray diffraction when the cellulose is cellulose type I crystal (derived from natural cellulose). Crystallinity (%) = ([Diffraction intensity from (200) plane with 2θ/deg. = 22.5] - [Diffraction intensity from amorphous with 2θ/deg. = 18]) / [Diffraction intensity from (200) plane with 2θ/deg. = 22.5] × 100

In addition, regarding the crystallinity, when the cellulose is a cellulose type II crystal (derived from regenerated cellulose), it can be obtained by the following formula based on the absolute peak intensity h0 at 2θ = 12.6° of the (110) plane peak belonging to the cellulose type II crystal in wide-angle X-ray diffraction and the peak intensity h1 of the baseline derived from the plane spacing. Crystallinity (%) = h1/h0×100

As the crystal form of cellulose, there are known types I, II, III, and IV, among which type I and type II are widely used, while type III and type IV are obtained on a laboratory scale and are not widely used on an industrial scale. As the cellulose nanofiber of the present invention, due to its relatively high structural mobility, and by dispersing the cellulose nanofiber in rubber, a molded body with a lower linear expansion coefficient and better strength and elongation during stretching, bending and deformation can be obtained, so it is preferably a cellulose nanofiber containing cellulose type I crystals or cellulose type II crystals, and more preferably a cellulose nanofiber containing cellulose type I crystals and a crystallinity of 55% or more.

Moreover, the degree of polymerization of the cellulose nanofiber is preferably 100 or more, more preferably 150 or more, more preferably 200 or more, more preferably 300 or more, more preferably 400 or more, more preferably 450 or more, and preferably 3500 or less, more preferably 3300 or less, more preferably 3200 or less, more preferably 3100 or less, and more preferably 3000 or less.

From the viewpoint of processability and mechanical properties, it is desirable to set the polymerization degree of cellulose nanofibers within the above range. From the viewpoint of processability, it is preferable that the polymerization degree is not too high, and from the viewpoint of mechanical properties, it is desirable that the polymerization degree is not too low.

The degree of polymerization of cellulose nanofibers refers to the average degree of polymerization measured by the reduced viscosity method based on copper ethylenediamine solution according to the confirmation test (3) described in the "Explanation of the Fifteenth Revised Edition of the Japanese Pharmacopoeia (published by Hirokawa Shoten)".

In one embodiment, the weight average molecular weight (Mw) of the cellulose nanofiber is 100,000 or more, preferably 200,000 or more. The ratio of the weight average molecular weight to the number average molecular weight (Mn) (Mw/Mn) is 6 or less, preferably 5.4 or less. The larger the weight average molecular weight, the fewer the number of terminal groups of the cellulose molecules. In addition, the ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn) represents the width of the molecular weight distribution, so the smaller the Mw/Mn, the fewer the number of terminal groups of the cellulose molecules. The end of the cellulose molecule becomes the starting point of thermal decomposition, and not only the weight average molecular weight of the cellulose molecule of the cellulose nanofiber is larger, but also when the weight average molecular weight is larger and the width of the molecular weight distribution is narrower, cellulose nanofibers with particularly high heat resistance and rubber compositions containing cellulose nanofibers and rubber can be obtained. From the perspective of the ease of obtaining the cellulose raw material, the weight average molecular weight (Mw) of the cellulose nanofiber can be, for example, less than 600,000 or less than 500,000. From the perspective of the ease of manufacturing the cellulose nanofiber, the ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) can be, for example, greater than 1.5 or greater than 2. Mw can be controlled within the above range by: selecting a cellulose raw material with a Mw that matches the purpose; appropriately performing physical treatment and/or chemical treatment on the cellulose raw material within an appropriate range. Mw/Mn can also be controlled within the above range by: selecting a cellulose raw material with a Mw/Mn that matches the purpose; appropriately performing physical treatment and/or chemical treatment on the cellulose raw material within an appropriate range. The Mw and Mw/Mn of the cellulose raw material can each be within the above range in one embodiment. In both cases of controlling Mw and controlling Mw/Mn, the above-mentioned physical treatments include dry or wet pulverization using a fine fluid homogenizer, ball mill, pan mill, etc.; physical treatments that apply mechanical forces such as impact, shearing, pounding, and friction using a pestle, homogenizer, high-pressure homogenizer, ultrasonic device, etc.; and the above-mentioned chemical treatments include cooking, bleaching, acid treatment, and regenerated fiberization.

Here, the weight average molecular weight and number average molecular weight of cellulose nanofibers are obtained by dissolving cellulose nanofibers in N,N-dimethylacetamide to which lithium chloride is added and then using N,N-dimethylacetamide as a solvent and gel permeation chromatography.

As a method for controlling the degree of polymerization (i.e., average degree of polymerization) or molecular weight of cellulose nanofibers, hydrolysis treatment can be cited. Through hydrolysis treatment, the depolymerization of amorphous cellulose inside the cellulose nanofibers proceeds, thereby reducing the average degree of polymerization. In addition, through hydrolysis treatment, the above-mentioned amorphous cellulose and impurities such as hemicellulose or lignin are removed together, so that the inside of the fiber becomes porous.

There is no particular limitation on the method of hydrolysis, and examples thereof include acid hydrolysis, alkaline hydrolysis, hot water hydrolysis, steam purification, microwave decomposition, etc. These methods may be used alone or in combination of two or more. In the method of acid hydrolysis, for example, α-cellulose obtained from fibrous plants in the form of pulp is used as a cellulose raw material, and an appropriate amount of protonic acid, carboxylic acid, Lewis acid, polyacid, etc. is added to the cellulose raw material while it is dispersed in an aqueous medium, and the mixture is heated while being stirred, thereby making it easy to control the average degree of polymerization. The reaction conditions such as temperature, pressure, time, etc. at this time vary depending on the type of cellulose, cellulose concentration, acid type, acid concentration, etc., but are all appropriately prepared in a manner to achieve the target average degree of polymerization. For example, the following conditions can be cited: using a 2 mass % or less aqueous solution of mineral acid, at a temperature of 100°C or more and under pressure, to treat cellulose nanofibers for more than 10 minutes. Under these conditions, the acid and other catalyst components penetrate into the interior of the cellulose nanofibers and promote hydrolysis, the amount of catalyst components used is reduced, and subsequent purification becomes easier. Furthermore, the dispersion of the cellulose raw material during hydrolysis can contain a small amount of organic solvent in addition to water within a range that does not damage the effect of the present invention.

In addition to hemicellulose, alkali-soluble polysaccharides that can be contained in cellulose nanofibers also include β-cellulose and γ-cellulose. Regarding alkali-soluble polysaccharides, the industry can understand that it is the component obtained as the alkali-soluble part of the whole cellulose obtained by solvent extraction and chlorine treatment of plants (such as wood) (that is, the component excluding α-cellulose in the whole cellulose). Alkali-soluble polysaccharides are polysaccharides containing hydroxyl groups, which have poor heat resistance and may cause the following abnormal conditions, such as decomposition when heated; yellowing during heat aging; resulting in a decrease in the strength of cellulose nanofibers, etc. Therefore, the content of alkali-soluble polysaccharides in cellulose nanofibers is preferably less.

In one embodiment, from the perspective of obtaining good dispersibility of cellulose nanofibers, the average content of alkali-soluble polysaccharides in cellulose nanofibers is preferably 20 mass % or less, or 18 mass % or less, or 15 mass % or less, or 12 mass % or less relative to 100 mass % of cellulose nanofibers. From the perspective of ease of manufacturing cellulose nanofibers, the above content may also be 1 mass % or more, or 2 mass % or more, or 3 mass % or more.

The average content of alkali-soluble polysaccharides can be obtained by the method described in the non-patent literature (Wood Science Experiment Guide, edited by the Japan Wood Society, pages 92-97, 2000), which can be obtained by subtracting the α-cellulose content from the total cellulose content (Wise method). In addition, this method is understood in the industry as a method for determining the amount of hemicellulose. The alkali-soluble polysaccharide content is calculated three times for each sample, and the calculated alkali-soluble polysaccharide content is averaged as the average alkali-soluble polysaccharide content.

In one embodiment, from the viewpoint of avoiding the decrease in heat resistance of cellulose nanofibers and the accompanying discoloration, the average content of the acid-insoluble components in the cellulose nanofibers is preferably 10% by mass or less, or 5% by mass or less, or 3% by mass or less relative to 100% by mass of the cellulose nanofibers. From the viewpoint of the ease of manufacturing the cellulose nanofibers, the above content may also be 0.1% by mass or more, or 0.2% by mass or more, or 0.3% by mass or more.

The average content of acid-insoluble components is quantified using the Klason method described in the non-patent literature (Guide to Experimental Wood Science, edited by the Japan Wood Society, pages 92-97, 2000). Furthermore, this method is understood in the industry as a method for determining the amount of lignin. After the sample is stirred in a sulfuric acid solution to dissolve cellulose and hemicellulose, it is filtered using glass fiber filter paper, and the resulting residue is an acid-insoluble component. The acid-insoluble component content is calculated based on the weight of the acid-insoluble component, and then the acid-insoluble component content calculated for the three samples is averaged as the average acid-insoluble component content.

From the viewpoint of being able to exert the heat resistance and mechanical strength desired in automotive applications, the thermal decomposition starting temperature (T _D ) of the cellulose nanofiber is 270° C. or higher, preferably 275° C. or higher, more preferably 280° C. or higher, and further preferably 285° C. or higher in one embodiment. The higher the thermal decomposition starting temperature, the better, but from the viewpoint of the ease of manufacturing the cellulose nanofiber, it may be, for example, 320° C. or lower, or 300° C. or lower.

In the present invention, _TD is a value obtained from a curve chart with temperature on the horizontal axis and weight residual rate % on the vertical axis in thermogravimetric (TG) analysis. The weight of cellulose nanofiber at 150°C (a state where water is basically removed) (weight loss 0wt%) is taken as the starting point, and the temperature is continuously raised to obtain a straight line passing through the temperature at 1wt% weight loss (T1 _% ) and the temperature at 2wt% weight loss (T2 _% ). The temperature at the intersection of the straight line and the horizontal line (baseline) passing through the starting point of weight loss 0wt% is defined as _TD .

The 1% weight loss temperature (T _1% ) is the temperature at which the weight is reduced by 1% by weight starting from 150°C when the temperature is continuously raised by the above-mentioned _TD method.

The 250°C weight loss rate of cellulose nanofibers (T _{250 °C} ) is the weight loss rate of cellulose nanofibers after being kept at 250°C under nitrogen flow for 2 hours in TG analysis.

(Chemical modification) The cellulose nanofiber may be a chemically modified cellulose nanofiber. The cellulose nanofiber may be chemically modified in advance at the stage of raw material pulp or cotton lint, during the defibration process, or after the defibration process, or may be chemically modified during or after the pulp preparation step, or during or after the drying (granulation) step.

As a modifying agent for cellulose nanofibers, compounds that react with the hydroxyl groups of cellulose can be used, such as esterifying agents, etherifying agents, and silanizing agents. On the other hand, modifying agents with polar groups such as carboxylic acids and phosphates have a tendency to reduce heat resistance due to the introduction of ionic groups (such as carboxyl groups) into cellulose nanofibers, and also have a tendency to reduce the fiber diameter after defiberization. Therefore, from the perspective of the reinforcing effect as a filler, it is better not to use a modifying agent. In a preferred embodiment, chemical modification is acylation using an esterifying agent, and acetylation is particularly preferred. As the esterifying agent, acetyl halides, acid anhydrides, vinyl carboxylates, and carboxylic acids are preferred.

The acyl halide may be at least one selected from the group consisting of compounds represented by the following formula: R ¹ -C(=O)-X (wherein R ¹ represents an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 24 carbon atoms, or an aryl group having 6 to 24 carbon atoms, and X represents Cl, Br, or I) Specific examples of the acyl halide include acetyl chloride, acetyl bromide, acetyl iodide, propionyl chloride, propionyl bromide, propionyl iodide, butyryl chloride, butyryl bromide, butyryl iodide, benzyl chloride, benzyl bromide, benzyl iodide, etc., but the present invention is not limited thereto. Among them, acyl chlorides are preferably used in terms of reactivity and operability. Furthermore, in the reaction of acetyl halide, one or more alkaline compounds may be added to act as a catalyst and neutralize the acidic substance produced as a by-product. Examples of alkaline compounds include, but are not limited to, tertiary amine compounds such as triethylamine and trimethylamine, and nitrogen-containing aromatic compounds such as pyridine and dimethylaminopyridine.

As the acid anhydride, any appropriate acid anhydride can be used. For example, the anhydrides of saturated aliphatic monocarboxylic acids such as acetic acid, propionic acid, (iso)butyric acid, and valeric acid; the anhydrides of unsaturated aliphatic monocarboxylic acids such as (meth)acrylic acid and oleic acid; the anhydrides of alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid and tetrahydrobenzoic acid; the anhydrides of aromatic monocarboxylic acids such as benzoic acid and 4-methylbenzoic acid; the anhydrides of saturated aliphatic dicarboxylic acids such as succinic acid and adipic acid as dicarboxylic acid anhydrides; unsaturated aliphatic dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride; alicyclic dicarboxylic acid anhydrides such as 1-cyclohexene-1,2-dicarboxylic anhydride, hexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride; and aromatic dicarboxylic anhydrides such as phthalic anhydride and naphthalene dicarboxylic anhydride; As polycarboxylic acid anhydrides with a valence of more than 3, for example, trimellitic anhydride, pyromellitic anhydride and other polycarboxylic acids (anhydrides) etc. Furthermore, in the reaction of the acid anhydride, one or more of the following compounds may be added as catalysts: acidic compounds such as sulfuric acid, hydrochloric acid, phosphoric acid, etc.; or Lewis acid (for example, Lewis acid compounds represented by MYn, wherein M represents a semimetallic element such as B, As, Ge; or a metal element such as Al, Bi, In; or a transition metal element such as Ti, Zn, Cu; or an ytterbium element, n is an integer equivalent to the atomic valence of M, representing 2 or 3, and Y represents a halogen atom, OAc, _OCOCF3 , _ClO4 , _SbF6 , _PF6 or _OSO2CF3 (OTf)); or alkaline compounds such as triethylamine and _pyridine .

The carboxylic acid vinyl ester is preferably a carboxylic acid vinyl ester represented by the formula: R-COO-CH= _CH2 {wherein R is any one of an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, or an aryl group having 6 to 24 carbon atoms}. The carboxylic acid vinyl ester is more preferably at least one selected from the group consisting of vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl cyclohexanecarboxylate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pivalate, vinyl caprylate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl caprylate, vinyl benzoate, and vinyl cinnamate. When the esterification reaction is carried out using vinyl carboxylate, one or more selected from the group consisting of alkali metal hydroxides, alkali earth metal hydroxides, alkali metal carbonates, alkali earth metal carbonates, alkali metal bicarbonates, primary to tertiary amines, quaternary ammonium salts, imidazole and its derivatives, pyridine and its derivatives, and alkoxides may be added as a catalyst.

Examples of the alkali metal hydroxide and alkali earth metal hydroxide include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide, etc. Examples of the alkali metal carbonate, alkali earth metal carbonate, and alkali metal bicarbonate include lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, and cesium bicarbonate.

The primary to tertiary amines refer to primary amines, diamines, and tertiary amines, and specific examples thereof include ethylenediamine, diethylamine, proline, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,3-propylenediamine, N,N,N',N'-tetramethyl-1,6-hexanediamine, tris(3-dimethylaminopropyl)amine, N,N-dimethylcyclohexylamine, triethylamine, and the like.

Examples of imidazole and its derivatives include 1-methylimidazole, 3-aminopropylimidazole, carbonyldiimidazole and the like.

Examples of pyridine and its derivatives include N,N-dimethyl-4-aminopyridine and picolinidine.

Examples of the alkoxide include sodium methoxide, sodium ethoxide, potassium tert-butoxide, and the like.

As the carboxylic acid, there can be cited: at least one selected from the group consisting of compounds represented by the following formula. R-COOH (wherein, R represents an alkyl group having 1 to 16 carbon atoms, an alkenyl group having 2 to 16 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, or an aryl group having 6 to 16 carbon atoms)

Specific examples of the carboxylic acid include at least one selected from the group consisting of acetic acid, propionic acid, butyric acid, caproic acid, cyclohexanecarboxylic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, pivalic acid, methacrylic acid, crotonic acid, caprylic acid, benzoic acid, and cinnamic acid.

Among the carboxylic acids, at least one selected from the group consisting of acetic acid, propionic acid, and butyric acid is preferred from the viewpoint of reaction efficiency, and acetic acid is particularly preferred. Furthermore, in the reaction of the carboxylic acid, one or more of the following compounds may be added as a catalyst: an acidic compound such as sulfuric acid, hydrochloric acid, phosphoric acid, or a Lewis acid (e.g., a Lewis acid compound represented by MYn, wherein M represents a semimetallic element such as B, As, Ge, or a semimetallic element such as Al, Bi, In, or a transition metal element such as Ti, Zn, Cu, or an yttrium element, wherein n is an integer equivalent to the atomic valence of M, representing 2 or 3, and Y represents a halogen atom, OAc, OCOCF ₃ , ClO ₄ , SbF ₆ , PF ₆ or OSO ₂ CF ₃ (OTf)); or an alkaline compound such as triethylamine or pyridine.

Among the esterification reactants, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid is preferred, and acetic anhydride and vinyl acetate are particularly preferred, particularly preferred.

When the cellulose nanofibers are chemically modified (for example, hydrophobized by acylation), there is a tendency that the cellulose nanofibers have good dispersibility in rubber. However, the cellulose nanofibers of the present invention can also show good dispersibility in rubber even if they are unsubstituted or have a low degree of substitution.

In one embodiment, the degree of substitution of the cellulose nanofiber is 0 (i.e., unsubstituted). Alternatively, in one embodiment, from the perspective of obtaining chemically modified cellulose nanofibers with a higher thermal decomposition onset temperature, the degree of substitution (DS) of the acyl group of the cellulose nanofiber may be greater than 0, or greater than 0.1, or greater than 0.2, or greater than 0.25, or greater than 0.3, or greater than 0.5. In addition, by leaving the unmodified cellulose skeleton in the esterified cellulose nanofibers, the esterified cellulose nanofibers having both the higher tensile strength and dimensional stability derived from cellulose and the higher thermal decomposition starting temperature derived from chemical modification can be obtained. The acyl substitution degree (DS) of the cellulose nanofibers can be 1.2 or less, or 1.0 or less, or 0.8 or less, or 0.7 or less, or 0.6 or less, or 0.5 or less.

When the modification group of chemically modified cellulose nanofibers is an acyl group, the acyl substitution degree (DS) can be calculated based on the peak intensity ratio of the peak derived from the acyl group and the peak derived from the cellulose backbone from the attenuated total reflectance (ATR) infrared absorption spectrum of the esterified cellulose nanofibers. The peak of the absorption band based on C=O of the acyl group appears at 1730 cm ^-1 , and the peak of the absorption band based on CO of the cellulose backbone chain appears at 1030 cm ^-1 . The DS of the esterified cellulose nanofibers can be obtained by preparing a correlation graph of the DS obtained by the solid NMR measurement of the esterified cellulose nanofibers described below and the modification rate (IR index 1030) defined as the ratio of the peak intensity of the absorption band of C=O based on the acyl group to the peak intensity of the absorption band of CO of the cellulose backbone chain, and using the calibration curve substitution degree DS = 4.13 × IR index (1030) calculated from the correlation graph.

The content of cellulose nanofibers in the rubber composition is preferably 0.5 mass % or more, 1 mass % or more, or 3 mass % or more from the viewpoint of obtaining a good reinforcing effect based on the cellulose nanofibers, and is preferably 80 mass % or less, 60 mass % or less, 33 mass % or less, 30 mass % or less, 20 mass % or less, or 10 mass % or less from the viewpoint of obtaining a rubber molded body having good rubber elasticity.

<The first rubber component (liquid rubber)> In the present invention, liquid rubber refers to a substance that is fluid at 23°C and forms a rubber elastomer by crosslinking (more specifically, vulcanization) and/or chain expansion. That is, the liquid rubber is an uncured substance in one state. Moreover, the so-called fluidity in one state refers to the following situation: liquid rubber dissolved in cyclohexane is added to a small glass bottle with a cylinder diameter of 21 mm × a total length of 50 mm at 23°C and then dried, thereby filling the small glass bottle with liquid rubber to a height of 1 mm and sealing it, and the small glass bottle is turned upside down. After standing for 24 hours in this state, it can be confirmed that the substance moves more than 0.1 mm in the height direction. Liquid rubber may have a monomer composition of general rubber, and preferably has a relatively low molecular weight from the viewpoint of ease of operation and good dispersion of cellulose nanofibers. The liquid rubber has a number average molecular weight (Mn) of 80,000 or less in one embodiment, so it is in liquid form. Furthermore, in the present invention, the molecular weight and molecular weight distribution of the rubber component are obtained by measuring the chromatogram using a gel permeation chromatography method in which three columns using polystyrene gel as a filler are connected, and using standard polystyrene and calculating by a calibration curve. Furthermore, tetrahydrofuran is used as a solvent.

When the rubber composition is cured to obtain a cured rubber, it is desirable that the liquid rubber vulcanizes during curing from the viewpoint of improving the mechanical properties of the cured rubber.

The number average molecular weight (Mn) of the liquid rubber is preferably 1,000 or more, 1,500 or more, or 2,000 or more from the viewpoint of obtaining a rubber composition having excellent storage modulus and dispersion of the matrix component in the rubber composite, and is preferably 80,000 or less, 50,000 or less, 40,000 or less, 30,000 or less, or 10,000 or less from the viewpoint of having high fluidity suitable for dispersing cellulose nanofibers well in the liquid rubber and that the liquid rubber does not become too hard after curing and has good rubber elasticity.

The weight average molecular weight (Mw) of the liquid rubber is preferably 1,000 or more, or 2,000 or more, or 4,000 or more from the viewpoint of obtaining a rubber composition having excellent storage modulus and dispersion of the matrix component in the rubber composite. It is preferably 240,000 or less, or 150,000 or less, or 30,000 or less from the viewpoint of having high fluidity suitable for dispersing cellulose nanofibers well in the liquid rubber and that the liquid rubber does not become too hard after curing and has good rubber elasticity.

The ratio (Mw/Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) of the liquid rubber is preferably 1.5 or more, 1.8 or more, or 2.0 or more in terms of being able to highly balance multiple properties of the rubber molded product (in one embodiment, highly balance the storage modulus and rubber elasticity of the rubber molded product) by making the molecular weight uneven to a certain extent. In terms of being able to stably obtain the desired physical properties of the rubber molded product without making the molecular weight uneven too much, it is preferably 10 or less, 8 or less, or 5 or less.

The liquid rubber may be a covalent diene polymer or a non-covalent diene polymer or a hydrogenated product thereof. The polymer or its hydrogenated product may also be an oligomer. In one embodiment, the liquid rubber may have reactive groups (e.g., one or more selected from the group consisting of hydroxyl, carboxyl, isocyanate, sulfhydryl, amine and halogen) at both ends, and thus may be bifunctional. The reactive groups contribute to the crosslinking and/or chain expansion of the liquid rubber.

[Copolymers of Diene] Copolymers of Diene may be homopolymers, copolymers of two or more copolymers of Diene monomers, or copolymers of a Copolymer of a Diene monomer and other monomers. Copolymers may be random or block.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, and 1,3-hexadiene. One of these monomers may be used alone or two or more thereof may be used in combination.

In one embodiment, the covalent diene polymer is a copolymer of the covalent diene monomer and an aromatic vinyl monomer. As the aromatic vinyl monomer, any monomer that can copolymerize with the covalent diene monomer is not particularly limited, and examples thereof include styrene, m- or p-methylstyrene, α-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinylethylbenzene, vinylxylene, vinylnaphthalene, diphenylethylene, and divinylbenzene. One of them may be used alone, or two or more thereof may be used in combination. From the viewpoint of the molding processability of the rubber composite and the impact resistance of the molded article, styrene is preferred.

Examples of random copolymers include butadiene-isoprene random copolymers, butadiene-styrene random copolymers, isoprene-styrene random copolymers, and butadiene-isoprene-styrene random copolymers. Examples of the composition distribution of each monomer in the copolymer chain include completely random copolymers that are statistically close to random composition and conical (gradient) random copolymers that have a gradient in composition distribution. The bonding mode of the conjugated diene polymer, i.e., the composition of 1,4-bonding, 1,2-bonding, etc., may be uniform or different between molecules.

The block copolymer may be a copolymer comprising more than two blocks. For example, the block A of the aromatic vinyl monomer and the block of the co-conjugated diene monomer and/or the block of the copolymer of the aromatic vinyl monomer and the co-conjugated diene monomer, i.e., the block B, may form a block copolymer having a structure such as A-B, A-B-A, A-B-A-B. Furthermore, the boundaries of each block may not necessarily need to be clearly distinguished. For example, when the block B is a copolymer of the aromatic vinyl monomer and the co-conjugated diene monomer, the aromatic vinyl monomer in the block B may be uniformly or conically distributed. In addition, there may be a plurality of uniformly distributed portions of the aromatic vinyl monomer and/or a conical distributed portion in the block B. Furthermore, there may also be a plurality of chain segments with different aromatic vinyl monomer contents in the block B. When there are a plurality of blocks A and B in the copolymer, their molecular weights and compositions may be the same or different.

The block copolymer may be a mixture of two or more types that differ from each other in one or more of the bonding mode, molecular weight, type of aromatic vinyl compound, type of conjugated diene compound, 1,2-vinyl content or the total amount of 1,2-vinyl content and 3,4-vinyl content, aromatic vinyl compound component content, hydrogenation rate, etc.

The vinyl bond content (e.g., 1,2- or 3,4-bonds of butadiene) in the conjugated diene bond unit in the conjugated diene polymer is preferably 10 mol% to 75 mol%, or 13 mol% to 65 mol%. The vinyl bond content (e.g., 1,2-bond content of butadiene) in the conjugated diene bond unit can be determined by the ¹³ C-NMR method (quantitative mode). That is, by integrating the following peak areas appearing in ¹³ C-NMR, a value proportional to the carbon content of each structural unit can be obtained, and the result can be converted into the mass % of each structural unit. Styrene 145-147 ppm Ethylene 110-116 ppm Diene (cis) 24-28 ppm Diene (trans) 29-33 ppm

In the copolymer of the covalent diene monomer and the aromatic vinyl monomer, the amount of the aromatic vinyl monomer bonded to the covalent diene monomer (also referred to as the aromatic vinyl bond amount in the present invention) relative to the total mass of the covalent diene polymer is preferably 5.0 mass% to 70 mass%, or 10 mass% to 50 mass%. The aromatic vinyl bond amount can be obtained by the ultraviolet absorbance of the phenyl group, and the covalent diene bond amount can also be obtained based on the ultraviolet absorbance of the phenyl group.

Examples of the hydrogenated product of the covalent diene polymer include the hydrogenated products of the covalent diene polymer exemplified above, such as hydrogenated products of butadiene homopolymer, isoprene homopolymer, styrene-butadiene copolymer, and acrylonitrile-butadiene copolymer.

[Non-conjugated diene polymers] Non-conjugated diene polymers may be homopolymers, or may be copolymers of two or more non-conjugated diene monomers or copolymers of non-conjugated diene monomers and other monomers. Copolymers may be random or block. Examples of non-conjugated diene polymers include: Olefin polymers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, and ethylene-α-olefin copolymers; Butyl rubber, brominated butyl rubber, acrylic rubber, fluororubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylate-conjugated diene copolymer rubber, urethane rubber, polysulfide rubber, etc.

In the ethylene-α-olefin copolymer, examples of monomers copolymerizable with the ethylene unit include propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecene-1, isobutylene, and the like. Aromatic vinyl monomers such as styrene and substituted styrene; ester vinyl monomers such as vinyl acetate, acrylate, methacrylate, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl methacrylate; nitrogen-containing vinyl monomers such as acrylamide, allylamine, vinyl-p-aminobenzene, acrylonitrile; dienes such as butadiene, cyclopentadiene, 1,4-hexadiene, isoprene, etc.

Preferred is a copolymer of ethylene and one or more α-olefins having 3 to 20 carbon atoms, more preferably a copolymer of ethylene and one or more α-olefins having 3 to 16 carbon atoms, and most preferably a copolymer of ethylene and one or more α-olefins having 3 to 12 carbon atoms. In addition, from the viewpoint of exhibiting impact resistance, the molecular weight of the ethylene-α-olefin copolymer is preferably 10,000 or more, more preferably 10,000 to 100,000, more preferably 10,000 to 80,000, and more preferably 20,000 to 60,000. In addition, from the viewpoint of taking both fluidity and impact resistance into consideration, the molecular weight distribution (weight average molecular weight/number average molecular weight: Mw/Mn) is preferably 3 or less, and more preferably 1.8 to 2.7.

Furthermore, from the viewpoint of workability during processing, the preferred content of ethylene units in the ethylene-α-olefin copolymer is 30 to 95% by mass based on the total amount of the ethylene-α-olefin copolymer.

Such preferred ethylene-α-olefin copolymers can be produced by the production methods described in, for example, Japanese Patent Publication No. 4-12283, Japanese Patent Publication No. 60-35006, Japanese Patent Publication No. 60-35007, Japanese Patent Publication No. 60-35008, Japanese Patent Publication No. 5-155930, Japanese Patent Publication No. 3-163088, U.S. Patent No. 5,272,236, and the like.

In one embodiment, the liquid rubber includes one or more selected from the group consisting of diene rubber (the above-mentioned covalent diene polymer in one embodiment), silicone rubber, urethane rubber, polysulfide rubber, and hydrogenated products thereof.

When the rubber composition is uniformly dispersed in the base rubber component of the rubber composite, it is advantageous that the viscosity of the liquid rubber at 80° C. is below a predetermined value. From the perspective of making the rubber composition well dispersed in the matrix rubber component in the rubber composite and making the cellulose nanofibers well dispersed in the liquid rubber, the viscosity of the liquid rubber at 80°C is preferably 1,000,000 mPa·s or less, or 500,000 mPa·s or less, or 250,000 mPa·s or less, or 100,000 mPa·s or less. From the perspective of obtaining a rubber composite with excellent physical properties (especially storage modulus), it is preferably 50 mPa·s or more, or 100 mPa·s or more, or 300 mPa·s or more.

Regarding the viscosity of the liquid rubber at 25°C, from the perspective of dispersing the cellulose nanofibers well in the liquid rubber, it is preferably 1,000,000 mPa·s or less, or 500,000 mPa·s or less, or 200,000 mPa·s or less, and from the perspective of obtaining a rubber composite with excellent physical properties (especially storage modulus), it is preferably 100 mPa·s or more, or 300 mPa·s or more, or 500 mPa·s or more.

When dispersing cellulose nanofibers in liquid rubber, it is advantageous that the viscosity of the liquid rubber at 0°C is below a predetermined value. In terms of dispersing cellulose nanofibers well in liquid rubber, the viscosity of the liquid rubber at 0°C is preferably 2,000,000 mPa·s or less, or 1,000,000 mPa·s or less, or 400,000 mPa·s or less, and in terms of obtaining a rubber composite with excellent physical properties (especially storage modulus), it is preferably 200 mPa·s or more, or 600 mPa·s or more, or 1,000 mPa·s or more.

In terms of being able to disperse cellulose nanofibers well in the liquid rubber over a wide mixing temperature range, it is preferred that the temperature dependence of the viscosity of the liquid rubber is small. From this viewpoint, it is particularly preferred that all viscosities of the liquid rubber at 80°C, 25°C and 0°C are within the above range.

The viscosity of liquid rubber is measured using a B-type viscometer at a rotation speed of 10 rpm.

The content of the liquid rubber in the rubber composition is preferably 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 5% by mass or more, or 10% by mass or more from the viewpoint of well obtaining the above-mentioned advantages based on the liquid rubber, and is preferably 99% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less from the viewpoint of containing an appropriate amount of other components (cellulose nanofibers, etc.) and well obtaining the advantages based on these components.

In the rubber composition, the mass ratio of the cellulose nanofibers to 100 mass parts of the total of the cellulose nanofibers and the liquid rubber is, in one aspect, 1 mass part or more, or 5 mass parts or more, or 10 mass parts or more, or 20 mass parts or more, or 30 mass parts or more, or 33 mass parts or more, or 40 mass parts or more, or 50 mass parts or more, and in one aspect, 99 mass parts or less, or 95 mass parts or less, or 90 mass parts or less, or 80 mass parts or less, or 70 mass parts or less, or 60 mass parts or less, or 50 mass parts or less.

<Surfactant> In one embodiment, the rubber composition includes a surfactant. In one embodiment, the surfactant is a nonionic surfactant, a cationic surfactant, or a combination thereof. As the surfactant, a nonionic surfactant is preferred from the viewpoint of heat resistance. The nonionic surfactant and the cationic surfactant enter into the voids of the aggregate of cellulose nanofibers and make the aggregate porous. For example, if a nonionic surfactant and/or a cationic surfactant is infiltrated into the wet aggregate and then dried to form a dry body, the shrinkage during drying can be reduced compared to the dry body obtained by drying the aggregate without using the nonionic surfactant and the cationic surfactant, so that the cellulose nanofibers are well dispersed when the dry body is mixed with liquid rubber.

The nonionic surfactant is preferably a compound having a hydrophilic group and a hydrocarbon group, wherein the hydrophilic group is selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfonic acid group, and an amino group.

In one embodiment, the nonionic surfactant has an aliphatic group with 6 to 30 carbon atoms as the hydrophobic portion. The cellulose nanofibers of this embodiment typically form a broad aggregate, and as a result, the nonionic surfactant has good affinity with the rubber component due to the carbon chain of the hydrophobic portion, and because the carbon chain of the hydrophobic portion is not too long, it can easily enter the voids of the cellulose nanofiber aggregate, thereby making the aggregate porous. For example, if a nonionic surfactant is infiltrated into the wet aggregate and then dried to form a dried body, the shrinkage during drying can be reduced compared to the dried body obtained by drying the aggregate without using the nonionic surfactant, so that the cellulose nanofibers are well dispersed when the dried body is mixed with the rubber component.

The aliphatic group may be a chain or alicyclic or a combination thereof. From the perspective of obtaining good dispersibility of cellulose nanofibers in the rubber component, the carbon number of the aliphatic group is 6 or more, 8 or more, or 10 or more in one embodiment, and from the perspective of penetrability into the voids of the cellulose nanofiber aggregate, it is 30 or less, 25 or less, or 20 or less in one embodiment.

The nonionic surfactant preferably has one or more structures selected from the group consisting of ethylene oxide, glycerol and sorbitan (specifically, a repeating structure with one or more of them as a repeating unit) as the hydrophilic part. These structures are preferred in terms of showing high hydrophilicity and being easy to obtain various nonionic surfactants by combining with various hydrophobic parts. In the nonionic surfactant having the above hydrophilic part, the carbon number n of the hydrophobic part and the number m of the repeating units of the above hydrophilic part preferably satisfy the following formula: n>m from the perspective of obtaining good dispersibility of cellulose nanofibers in the rubber component. The repetition number m of the hydrophilic part is preferably 1 or more, 2 or more, 3 or more, or 5 or more from the viewpoint of good penetration of the non-ionic surfactant into the voids of the cellulose nanofiber aggregate, and is preferably 30 or less, 25 or less, 20 or less, or 18 or less from the viewpoint of obtaining good dispersibility of the cellulose nanofibers in the rubber component.

The nonionic surfactant is preferably one or more selected from the group consisting of compounds represented by the following general formula (1): R- _{( OCH2CH2 ) m} - _OH (1) [wherein R represents a monovalent aliphatic group having 6 to 30 carbon atoms, and m is a natural number less than the carbon number of R], and compounds represented by the following general formula (2): R1OCH2-(CHOH) ₄ - _CH2OR2 ( _{2 ) [wherein R1 and R2 each independently represent a hydrogen atom, an aliphatic group having 1 to 30 carbon atoms, -COR3 {wherein R3 represents an aliphatic group having 1 to 30 carbon atoms}, or -(CH2CH2O)y-R4 { wherein R4 represents a hydrogen atom or} an aliphatic group having 1 to 30 carbon atoms, and y is an integer of 1 to 30}].

In general formula ( ₁ ), R corresponds to the hydrophobic part, ( _OCH2CH2 ) (i.e. _, ethylene oxide unit) corresponds to the hydrophilic part. The carbon number of R and the repetition number m of ( _OCH2CH2 ) are preferably in the same range as the carbon number n of the hydrophobic part and the repetition number m of the hydrophilic part described above.

In the general formula (2), for each of R ₁ , R ₂ , R ₃ and R ₄ , the carbon number of the aliphatic group having 1 to 30 carbon atoms is preferably 6 or more, 8 or more, or 10 or more, and is preferably 24 or less, 20 or less, or 18 or less. In addition, y is 1 or more, preferably 2 or more, or 4 or more, and is preferably 30 or less, 25 or less, or 20 or less.

Examples of the cationic surfactant include benzyl ammonium chloride, alkyltrimethyl ammonium chloride, stearyl dimethyl ammonium chloride, stearyl trimethyl ammonium chloride, ethylsulfate lanolin fatty acid aminopropyl ethyl dimethyl ammonium, stearyl dimethyl benzyl ammonium chloride, stearylamine acetate, and coconut amine acetate.

The amount of the surfactant, or the amount of the nonionic surfactant, or the amount of the cationic surfactant, or the total amount of the nonionic surfactant and the cationic surfactant in the rubber composition is preferably 10 parts by mass or more, or 15 parts by mass or more, or 20 parts by mass or more, and is preferably 200 parts by mass or less, or 150 parts by mass or less, or 100 parts by mass or less, or 90 parts by mass or less, or 80 parts by mass or less, or 70 parts by mass or less, or 60 parts by mass or less, or 50 parts by mass or less, or 45 parts by mass or less, or 40 parts by mass or less, relative to 100 parts by mass of the cellulose nanofiber.

<Additional ingredients> In addition to the above-mentioned cellulose nanofibers, liquid rubber and surfactant, the rubber composition may further include additional ingredients. Examples of additional ingredients include: additional polymers, dispersants, organic or inorganic fillers, thermal stabilizers, antioxidants, antistatic agents, colorants, etc. Examples of additional polymers include: rubber components exemplified as the matrix components of the rubber composite below, thermoplastic elastomers, etc. The content ratio of any additional component in the rubber composition can be appropriately selected within the range that does not impair the desired effect of the present invention, for example, it can be 0.01 to 50% by mass, or 0.1 to 30% by mass.

<Production of rubber composition> The production method of the rubber composition is not particularly limited. The components constituting the rubber composition can be mixed using a stirring mechanism such as a rotary and revolving stirrer, a planetary stirrer, a homogenizer, a homogenizer, a screw stirrer, a rotary stirrer, an electromagnetic stirrer, an open drum, a Banbury stirrer, a single-shaft extruder, a double-shaft extruder, etc. to obtain the rubber composition. In addition, stirring can also be performed under heating to efficiently perform shearing. In terms of promoting dispersion by applying high shear force and pressure, a mixing method using a homogenizer is preferred. The order of adding the components during mixing is not limited, and examples thereof include: (1) a method of adding cellulose nanofibers, a surfactant, a liquid rubber, and any other components simultaneously and mixing them to obtain a rubber composition; (2) a method of mixing components other than liquid rubber in advance to obtain a premix, and then mixing the premix with liquid rubber to obtain a rubber composition. In addition, as an example of the method (2) above, the following method may be cited: By mixing cellulose nanofibers and a surfactant, the surfactant is infiltrated into the voids of the cellulose nanofiber aggregate, and then, liquid rubber is added and mixed to infiltrate the liquid rubber into the voids. In the method (2) above, the premix may be dried after the premix is obtained and before it is mixed with the liquid rubber. Alternatively, the rubber composition may be dried after it is obtained, or the following powder may be formed by controlling the drying conditions.

《Powder》 One aspect of the present invention is to provide a powder, which is composed of the rubber composition of the present invention. The powder may have one or more of the following properties. Thereby, the powder has excellent processing properties, and the cellulose nanofibers can show an excellent dispersion state in the rubber component.

<State of the cellulose nanofiber surface> In order for the cellulose nanofiber to be easily dispersed in the second rubber component or the third rubber component without agglomeration of the cellulose nanofiber in the powder of one embodiment, it is preferred that at least a portion of the surface of the cellulose nanofiber is covered by the first rubber component. In one embodiment, the state in which at least a portion of the surface of the cellulose nanofiber is covered by the first rubber component refers to the following state: the first rubber component is in direct contact with the cellulose nanofiber, and the average length of the contact portion is more than twice the average fiber diameter of the cellulose nanofiber. The surface of the cellulose nanofibers in the powder is observed by an electron microscope (a scanning electron microscope in one embodiment) or an atomic force microscope in a state where the surface is covered by the first rubber component. However, when both the electron microscope and the atomic force microscope can be used to confirm, the electron microscope is used to confirm. The above average fiber diameter is a value measured by the method of the present invention using the powder as a measurement sample. The above average length of the contact portion is measured by an electron microscope (a scanning electron microscope in one embodiment) or an atomic force microscope using the powder as a measurement sample. Specifically, in an observation field with a magnification adjusted so that at least 30 fiber nanofibers can be observed, the length of the contact portion with the first rubber component is measured for each of the 30 randomly selected fiber nanofibers and the quantitative average is calculated, and then the quantitative average is taken for the 30 fibers and used as the average length of the contact portion.

<Loose density> In one embodiment, the loose density of the powder is preferably 0.01 g/cm 3 or more, or 0.05 g/cm ³ or more, or 0.10 g/cm ³ or more, or 0.15 g/cm 3 or more, or 0.20 g/cm ^{3 or} more, from the viewpoint of good fluidity of the powder and excellent feeding property to the kneading machine, and inhibiting the migration of the surfactant to the rubber. From the viewpoint of easy disintegration of the powder in the rubber so that the cellulose nanofiber can be well dispersed in the rubber, and the powder is not too ^heavy to avoid poor mixing of the powder and the rubber, it is preferably 0.50 g/cm ³ or less, or 0.40 g/cm ³ or less, or 0.30 g/cm ³ or less, or 0.25 g/cm 3 or less. ³ or less, or 0.20 g/cm ³ or less.

<Tap density> The tap density of the powder is controlled within a range that can be used to control the loose density and the degree of compression within an appropriate range. In one embodiment, it is preferably 0.01 g/cm ³ or more, or 0.05 g/cm ³ or more, or 0.10 g/cm ³ or more, or 0.15 g/cm ³ or more, or 0.20 g/cm ³ or more, and is preferably 1.00 g/cm ³ or less, or 0.80 g/cm ³ or less, or 0.70 g/cm ³ or less, or 0.60 g/cm ³ or less, or 0.50 g/cm ³ or less, or 0.40 g/cm ³ or less, or 0.30 g/cm ³ or less.

The above-mentioned loose density and tap density are values measured using a powder testing machine (model: PT-X) manufactured by Hosokawa Micron Co., Ltd. in the order described in the [Example] section of the present invention.

As a method for producing a powder, there can be exemplified a method including a slurry preparation step of preparing a slurry containing cellulose nanofibers and a liquid medium and a drying step of drying the slurry to form a powder.

(Slurry preparation step) In this step, slurry is prepared. As the liquid medium, a water-miscible organic solvent can be used, for example: alcohols with a boiling point of 50°C to 170°C (such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, 2-butanol, 3-butanol, etc.); ethers (such as propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (such as formic acid, acetic acid, lactic acid, etc.); esters (such as ethyl acetate, vinyl acetate, etc.); ketones (such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.), etc. In a typical embodiment, the liquid medium in the slurry is substantially only water. The slurry may be composed of cellulose nanofibers and a liquid medium, and may also contain a surfactant and/or a first rubber component, and any additional components.

Regarding the concentration of cellulose nanofibers in the slurry, from the perspective of process efficiency in the subsequent drying step, it is preferably 5 mass % or more, or 10 mass % or more, or 15 mass % or more, or 20 mass % or more, or 25 mass % or more. From the perspective of avoiding excessive increase in viscosity of the slurry and solidification caused by coagulation and maintaining good operability, it is preferably 60 mass % or less, or 55 mass % or less, or 50 mass % or less, or 45 mass % or less. For example, the production of cellulose nanofibers is mostly carried out in a dilute dispersion, but the concentration of cellulose nanofibers in the slurry can also be adjusted to the above-mentioned preferred range by concentrating such a dilute dispersion. When concentrating, methods such as vacuum filtration, pressure filtration, centrifugal dehydration, and heating can be used.

(Drying step) In this step, the slurry is dried under controlled drying conditions to form a powder. The ingredients other than cellulose nanofibers may be added before, during, and/or after drying the slurry. Drying devices such as spray dryers and extruders may be used for drying. The drying device may also be a commercially available product, such as a micro spray dryer (manufactured by Fujisaki Electric Co., Ltd.), a spray dryer (manufactured by Ohkawara Chemical Industry Co., Ltd.), a double-spindle extruder (manufactured by Nippon Steel Works), etc. In order to achieve the desired shape of the powder, it may be beneficial to appropriately control the drying speed, drying temperature, and/or pressure (decompression), especially the drying speed, among the drying conditions.

The drying rate, i.e., the amount of liquid medium removed per minute per 100 parts by mass of the slurry (parts by mass), may be, for example, 10%/minute or more, 50%/minute or more, or 100%/minute or more, from the viewpoint of rapidly drying the slurry to form a powder of a desired particle size; and may be, for example, 10,000%/minute or less, 1,000%/minute or less, or 500%/minute or less, from the viewpoint of avoiding excessive micronization of the cellulose nanofibers to inhibit the aggregation of the cellulose nanofibers and obtaining good operability. The drying rate is calculated according to the following formula: Drying rate (%/min) = (moisture content of slurry at the start of drying (mass %) - moisture content of powder at the end of drying (mass %)) / time required from the start of drying to the end of drying (minutes) The value obtained (i.e., the average value through the drying step). Here, the start of drying is the time when the slurry or cake to be dried is supplied to the device and the drying step is carried out at the target drying temperature, decompression, and shear rate. The drying time does not include the time for pre-mixing at a state where the drying temperature, decompression, and shear rate are different from the drying step. In addition, the end of drying refers to the time when the moisture content becomes less than 7% by mass for the first time after sampling at intervals of up to 10 minutes from the start of drying. In the case of a continuous drying device, the time required from the start of drying to the end of drying can be interpreted as the residence time. In the case of a spray dryer, the residence time can be calculated based on the heating air volume and the volume of the drying chamber. In addition, when using an extruder as a drying device, the residence time can be calculated based on the number of screw revolutions and the total number of screw pitches.

Regarding the drying temperature, from the viewpoint of drying efficiency and making the cellulose nanofibers appropriately agglomerate to form powders of the desired particle size, for example, it can be above 20°C, above 30°C, above 40°C, or above 50°C. From the viewpoint of making it difficult for the cellulose nanofibers and additional components to be thermally degraded and avoiding excessive micronization of the cellulose nanofibers, for example, it can be below 200°C, below 150°C, below 140°C, below 130°C, or below 100°C. The drying temperature is the temperature of the heat source in contact with the slurry, and is defined by, for example, the surface temperature of the temperature control jacket of the drying device, the surface temperature of the heating cylinder, or the temperature of the hot air.

Regarding the degree of reduced pressure, from the viewpoint of drying efficiency and making the cellulose nanofibers appropriately agglomerated to form a powder of a desired particle size, it can be -1 kPa or less, or -10 kPa or less, or -20 kPa or less, or -30 kPa or less, or -40 kPa or less, or -50 kPa or less, and from the viewpoint of avoiding excessive micronization of the cellulose nanofibers, it can be -100 kPa or more, or -95 kPa or more, or -90 kPa or more.

In the drying step, the retention time of the slurry at a temperature of 20°C to 200°C can be preferably set to 0.01 minutes to 10 minutes, or 0.05 minutes to 5 minutes, or 0.1 minutes to 2 minutes. By drying under such conditions, the cellulose nanofibers are dried rapidly, thereby generating a powder of the desired particle size.

For example, when a spray dryer is used, a spray mechanism (rotating disk, pressurized nozzle, etc.) is used to introduce the slurry into a drying chamber where hot air is flowing for drying. The slurry droplet size during the spray introduction can be, for example, 0.01 μm to 500 μm, or 0.1 μm to 100 μm, or 0.5 μm to 10 μm. The hot air can be an inert gas such as nitrogen, argon, or air. The hot air temperature can be, for example, 50°C to 300°C, or 80°C to 250°C, or 100°C to 200°C. The contact between the slurry droplets and the hot air in the drying chamber can be co-current, convection, or co-convection. Use a cyclone dust collector, a drum, etc. to collect the granular powder produced by the drying of the droplets.

In addition, for example, when an extruder is used, the slurry is fed from a hopper into a kneading section equipped with a screw, and the slurry is continuously conveyed by the screw in the kneading section under reduced pressure and/or heating, thereby drying the slurry. As the form of the screw, a conveying screw, a counterclockwise rotating screw, and a kneading disk can be combined in any order. The drying temperature can be, for example, 50°C to 300°C, or 80°C to 250°C, or 100°C to 200°C.

"Masterbatch" One aspect of the present invention provides a masterbatch, which includes the rubber composition of the present invention. In one aspect, the masterbatch is a mixture of the powder of the present invention and a second rubber component.

<Second rubber component> The second rubber component may be natural rubber, a conjugated diene polymer or a non-conjugated diene polymer or a hydrogenated product thereof. The above polymer or its hydrogenated product may be an oligomer. As the monomer composition of the second rubber component, the same monomer composition as described above for the liquid rubber may be exemplified. The second rubber component may be the above liquid rubber, or may be a rubber that is not a liquid rubber.

The covalent diene polymer as the second rubber component constituting the matrix component may be partially or completely hydrogenated. From the viewpoint of suppressing thermal degradation during processing, the hydrogenation rate of the hydrogenated product is preferably 50% or more, 80% or more, or 98% or more, and from the viewpoint of low temperature toughness, it is preferably 50% or less, 20% or less, or 0% (i.e., non-hydrogenated product).

In the covalent diene polymer as the second rubber component constituting the matrix component, the amount of vinyl bonds in the covalent diene bonding units (e.g., 1,2- or 3,4-bonds of butadiene) is preferably 5 mol% or more, or 10 mol% or more, or 13 mol% or more, or 15 mol% or more, and is preferably 80 mol% or less, or 75 mol% or less, or 65 mol% or less, or 50 mol% or less, or 40 mol% or less, from the viewpoint of suppressing crystallization of the soft segment.

In a preferred embodiment, the second rubber component includes at least one selected from the group consisting of styrene-butadiene rubber, butadiene rubber and isoprene rubber.

The number average molecular weight (Mn) of the second rubber component is preferably 100,000 or more, or 150,000 or more, or 200,000 or more from the viewpoint of obtaining a rubber composite having excellent storage modulus, and is preferably 800,000 or less, or 750,000 or less, or 700,000 or less, or 600,000 or less from the viewpoint of the ease of dispersion of cellulose nanofibers in the second rubber component and that the second rubber component does not become too hard after curing and has good rubber elasticity.

[Modified rubber] The second rubber component may also be a modified rubber, for example, a modified group such as an epoxy group, anhydride group, carboxyl group, aldehyde group, hydroxyl group, alkoxy group, amino group, amide group, imide group, nitro group, isocyanate group, hydroxyl group, etc. may be introduced into the above-mentioned covalent diene polymer or non-covalent diene polymer. Examples of modified rubbers include: epoxy-modified natural rubber, epoxy-modified butadiene rubber, epoxy-modified styrene butadiene rubber, carboxyl-modified natural rubber, carboxyl-modified butadiene rubber, carboxyl-modified styrene butadiene rubber, anhydride-modified natural rubber, anhydride-modified butadiene rubber, anhydride-modified styrene butadiene rubber, etc.

Regarding the amount of the modifying group relative to 100 mol% of all monomer units, from the viewpoint of affinity between the cellulose nanofiber and the second rubber component, it is preferably 0.1 mol% or more, or 0.2 mol% or more, or 0.3 mol% or more, and preferably 5 mol% or less, or 3 mol% or less. The amount of the modifying group can be confirmed by FT-IR (Fourier transform infrared spectroscopy), solid NMR (nuclear magnetic resonance), solution NMR, or by combining the pre-specified monomer composition with the quantitative analysis of the elements not contained in the unmodified rubber to calculate the molar ratio of the modifying group.

In the masterbatch, the content of the second rubber component is preferably 20 mass % or more, or 30 mass % or more, or 40 mass % or more, and is preferably 99 mass % or less, or 95 mass % or less, or 90 mass % or less.

[Thermoplastic elastomer] In one embodiment, the second rubber component may include a thermoplastic elastomer or be a thermoplastic elastomer. In the present invention, in one embodiment, the elastomer is a substance (specifically, a natural or synthetic polymer substance) that is an elastomer at room temperature (23°C). In addition, the so-called elastomer, in one embodiment, refers to a storage modulus of 1 MPa or more and 100 MPa or less at 23°C and 10 Hz measured by dynamic viscoelasticity measurement. The thermoplastic elastomer may be a covalent diene polymer or a non-covalent diene polymer, and in one embodiment is a crosslinked polymer. Suitable monomer compositions of thermoplastic elastomers may be the same as those described above in the items (covalent diene polymers) and (non-covalent diene polymers).

The number average molecular weight (Mn) of the thermoplastic elastomer is preferably 10,000 to 500,000, or 40,000 to 250,000, from the viewpoint of both impact strength and fluidity.

Thermoplastic elastomers may also have a core-shell structure. Examples of elastomers having a core-shell structure include a core in the form of a rubber particle and a shell formed on the outside of the core as a glassy coating. As the core, butadiene rubber, acrylic rubber, silicone-acrylic resin composite rubber, etc. are more suitable. In addition, as the shell, glassy polymers such as styrene resin, acrylonitrile-styrene copolymer, acrylic resin, etc. are more suitable.

From the viewpoint of further improving the compatibility with the rubber composition, the thermoplastic elastomer is preferably at least one selected from the group consisting of styrene-butadiene block copolymers, styrene-ethylene-butadiene block copolymers, styrene-ethylene-butylene block copolymers, styrene-butadiene-butylene block copolymers, styrene-isoprene block copolymers, styrene-ethylene-propylene block copolymers, styrene-isobutylene block copolymers, hydrogenated styrene-butadiene block copolymers, hydrogenated styrene-ethylene-butadiene block copolymers, hydrogenated styrene-butadiene-butylene block copolymers, hydrogenated styrene-isoprene block copolymers, and styrene homopolymers (polystyrene), and more preferably at least one selected from the group consisting of styrene-butadiene block copolymers, hydrogenated styrene-butadiene block copolymers, and polystyrene.

In one embodiment, at least a portion of the thermoplastic elastomer may have an acidic functional group. In the present invention, the thermoplastic elastomer having an acidic functional group means that the acidic functional group is added to the molecular skeleton of the elastomer via a chemical bond. In the present invention, the acidic functional group refers to a functional group that can react with a basic functional group, etc., and specific examples thereof include a hydroxyl group, a carboxyl group, a carboxylate group, a sulfonic group, an acid anhydride group, etc.

Regarding the amount of acidic functional groups added to the elastomer, from the viewpoint of affinity between cellulose nanofibers and elastomer components, based on 100% by mass of the elastomer, it is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and further preferably 0.2% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2% by mass or less. Furthermore, regarding the number of acidic functional groups, a calibration curve sample mixed with an acidic substance is measured in advance by an infrared absorption spectrometer, and a calibration curve is prepared in advance using the characteristic absorption band of the acid. The sample is measured based on the calibration curve, and the value obtained is the number of acidic functional groups.

Examples of the elastomer having an acidic functional group include an elastomer having a core-shell structure having a layer formed using acrylic acid or the like as a copolymer component as an outer shell; an elastomer which is a modified product obtained by grafting an α,β-unsaturated dicarboxylic acid or a derivative thereof onto an ethylene-α-olefin copolymer, a polyolefin, an aromatic compound-covalent diene copolymer, or an aromatic compound-covalent diene copolymer hydrogenate containing acrylic acid or the like as a monomer in the presence or absence of a peroxide; and the like.

In a preferred embodiment, the elastomer is an anhydride-modified elastomer.

Among them, more preferred is a modified product obtained by grafting an α,β-unsaturated dicarboxylic acid or a derivative thereof onto a polyolefin, an aromatic compound-covalent diene copolymer, or an aromatic compound-covalent diene copolymer hydrogenate in the presence or absence of a peroxide, and particularly preferred is a modified product obtained by grafting an α,β-unsaturated dicarboxylic acid or a derivative thereof onto an ethylene-α-olefin copolymer, or an aromatic compound-covalent diene block copolymer hydrogenate in the presence or absence of a peroxide.

Specific examples of the α,β-unsaturated dicarboxylic acid and its derivatives include maleic acid, fumaric acid, maleic anhydride, and fumaric anhydride, among which maleic anhydride is particularly preferred.

In one embodiment, the elastomer may be a mixture of an elastomer having an acidic functional group and an elastomer not having an acidic functional group. When the total of the elastomer having an acidic functional group and the elastomer not having an acidic functional group is set to 100 mass %, from the viewpoint of maintaining high toughness and good physical stability of the rubber composite, the elastomer having an acidic functional group is preferably 10 mass % or more, more preferably 20 mass % or more, further preferably 30 mass % or more, and most preferably 40 mass % or more. The upper limit is not particularly limited, and substantially all elastomers may be elastomers having an acidic functional group, but from the viewpoint of not causing problems in fluidity, it is preferably 80 mass % or less.

In the masterbatch, the content of the thermoplastic elastomer is preferably 20 mass % or more, or 30 mass % or more, and is preferably 99 mass % or less, or 95 mass % or less, or 90 mass % or less.

<Vulcanizing agent, vulcanization accelerator> When the masterbatch contains uncured rubber, the masterbatch typically contains a vulcanizing agent and may contain an arbitrary vulcanization accelerator. As the vulcanizing agent and the vulcanization accelerator, previously known ones can be appropriately selected according to the type of uncured rubber in the masterbatch. As the vulcanizing agent, organic peroxides, azo compounds, oxime compounds, nitroso compounds, polyamine compounds, sulfur, sulfur compounds, etc. can be used. As sulfur compounds, sulfur monochloride, sulfur dichloride, disulfide compounds, high molecular weight polysulfide compounds, etc. can be cited. The amount of the vulcanizing agent is preferably 0.01 to 20 parts by mass, or 0.1 to 15 parts by mass, relative to 100 parts by mass of the uncured rubber in the masterbatch.

Examples of the vulcanization accelerator include sulfenamide, guanidine, thiuram, aldehyde-amine, aldehyde-ammonia, thiazole, thiourea, and dithiocarbamate. In addition, zinc white, stearic acid, and the like may also be used as vulcanization aids. The amount of the vulcanization accelerator is preferably 0.01 to 20 parts by mass, or 0.1 to 15 parts by mass, relative to 100 parts by mass of the uncured rubber in the masterbatch.

[Rubber additives] The masterbatch may also contain various previously known rubber additives (stabilizers, softeners, anti-aging agents, etc.). As rubber stabilizers, one or more antioxidants such as 2,6-di-tert-butyl-4-hydroxytoluene (BHT), 3-(4'-hydroxy-3',5'-di-tert-butylphenyl) propionate, and 2-methyl-4,6-bis[(octylthio)methyl]phenol may be used. In addition, as rubber softeners, one or more processing oils, extender oils, etc. may be used. Among them, the masterbatch of this embodiment can form a soft molded body in one aspect, so a rubber softener may not be included in one aspect.

<Additional ingredients> The masterbatch may further contain additional ingredients as needed to improve its performance. Examples of additional ingredients include dispersants, organic or inorganic fillers, thermal stabilizers, antioxidants, antistatic agents, colorants, etc. The content ratio of any additional ingredient in the masterbatch is appropriately selected within the range that does not impair the desired effect of the present invention, for example, it may be 0.01 to 50% by mass, or 0.1 to 30% by mass.

In a preferred embodiment, the masterbatch comprises 10 to 50, 15 to 40, or 20 to 30 parts by mass of cellulose nanofibers relative to 100 parts by mass of the rubber component, and comprises 1 to 50, 2 to 40, or 3 to 30 parts by mass of a surfactant. Furthermore, the amount of the rubber component is the total amount of the rubber components present in the masterbatch (in one embodiment, the total amount of the first rubber component and the second rubber component). In one embodiment, the composition of the masterbatch can be the same as described above with respect to the rubber composition. In the masterbatch, the mass ratio (masterbatch/additional component) to the additional component (in one embodiment, the second rubber component) may be 1/99 to 99/1, or 5/95 to 95/5, or 10/90 to 90/10, or 20/80 to 80/20, or 30/70 to 70/30, or 40/60 to 60/40.

One aspect of the present invention is to provide a method for producing a masterbatch, which comprises the following steps: kneading the powder of the present invention with a second rubber component to obtain a masterbatch. The kneading conditions are not particularly limited, and for example, a Banbury mixer, an open drum, or other kneading machine commonly used in rubber kneading can be used.

《Rubber composite》 One aspect of the present invention also provides a rubber composite, which includes: the rubber composition of the present embodiment, and a matrix component (i.e., a component other than the rubber composition) (obtained by mixing them in one aspect). In a typical aspect, the rubber composite is derived from the powder or masterbatch of the present invention. In one aspect, the rubber composite includes the above-mentioned cellulose nanofibers, the above-mentioned liquid rubber and the above-mentioned surfactant, and further includes a third rubber component and any additional component as a matrix component. The third rubber component can be one or more selected from the group consisting of uncured rubber and thermoplastic elastomer.

In one embodiment, the rubber composite is a mixture of the powder of the present invention or the masterbatch of the present invention and a third rubber component. The specific suitable embodiment of the third rubber component may be the same as described above with respect to the second rubber component. The first, second and third rubber components may have different monomer component types, monomer component ratios and molecular weights (different types), or two or more of the first, second and third rubber components may have the same monomer component types, monomer component ratios and molecular weights (same type). In a preferred embodiment of the rubber composite, at least a portion of the surface of the cellulose nanofiber is coated by the first rubber component. The above-mentioned coating state is confirmed by the above-mentioned scanning electron microscope observation or atomic force microscope. However, in the case where the first rubber component and the second and/or third rubber components cannot be distinguished by scanning electron microscope observation and atomic force microscope observation, if at least a portion of the surface of the cellulose nanofiber is coated by the unidentified rubber component, it can be considered that at least a portion of the surface is coated by the first rubber component. In this case, the first rubber component and the second and/or third rubber component are of the same type, or even if they are of different types, their properties are very similar. Therefore, it is believed that by coating the cellulose nanofiber with the unidentified rubber component, the advantages obtained when the cellulose nanofiber is coated with the first rubber component can be expressed.

In one embodiment, the mass ratio of the powder to the third rubber component (powder/third rubber component) may be 1/99 to 99/1, or 5/95 to 95/5, or 10/90 to 90/10, or 20/80 to 80/20, or 30/70 to 70/30, or 40/60 to 60/40.

The mass ratio of the masterbatch to the third rubber component (masterbatch/third rubber component) may be 1/99 to 99/1, or 5/95 to 95/5, or 10/90 to 90/10, or 20/80 to 80/20, or 30/70 to 70/30, or 40/60 to 60/40 in one embodiment.

The rubber composite can be produced by a method comprising the steps of kneading the powder of the present invention and the third rubber component, or forming a masterbatch by the masterbatch production method of the present invention, and then kneading the masterbatch and the third rubber component to obtain a rubber composite. The above kneading conditions are not particularly limited, and for example, a Banbury mixer, an open drum, or other kneading machine commonly used in rubber kneading can be used.

The content of cellulose nanofiber in the rubber composite is preferably 0.5 mass % or more, or 1 mass % or more, or 2 mass % or more, and is preferably 30 mass % or less, or 20 mass % or less, or 15 mass % or less, or 10 mass % or less.

The total content of the polymer components in the rubber compound (in one embodiment, the total content of the first, second and third rubber components) is preferably 1 mass % or more, or 2 mass % or more, or 5 mass % or more, and is preferably 99 mass % or less, or 95 mass % or less, or 90 mass % or less.

The total mass ratio of cellulose nanofibers to polymer components in the rubber composite is preferably 1/99 to 50/50, or 2/98 to 40/60, or 3/97 to 30/70.

The content of the surfactant in the rubber composite may be 0.1 mass % or more, 0.5 mass % or more, or 1 mass % or more in one embodiment, and may be 10 mass % or less, 5 mass % or less, or 1 mass % or less in one embodiment.

In one aspect of the rubber compound, the amount of the vulcanizing agent and/or vulcanization accelerator for the uncured rubber in the rubber compound may be in the same range as exemplified as the amount of the vulcanizing agent and/or vulcanization accelerator for the uncured rubber in the masterbatch.

In one aspect of the rubber compound, the amount of the rubber additive and the additional component in the rubber compound may be in the same range as exemplified as the amount in the masterbatch.

《Rubber cured product and molded body》 One aspect of the present invention provides a rubber cured product, which is a cured product of a curable component of the rubber composition of the present invention. In one aspect, the desired molded body is manufactured by molding the rubber composition of the present invention together with other desired components into a desired shape. In one aspect, the rubber composition of the present invention can be mixed with a third rubber component and optionally with additional components to form a rubber composite, and the rubber composite can be molded into a desired shape alone or together with other components to manufacture the desired molded body. The combination method and molding method of the formulated components are not particularly limited and can be selected according to the desired molded body. As molding methods, the following methods can be cited, but are not limited to them: (1) A method in which a rubber composition or a masterbatch contains uncured rubber, and the uncured rubber is hardened before, during, and/or after molding the rubber composition or the masterbatch alone or together with an additional component, thereby obtaining a molded body containing a rubber hardened product; (2) A method in which a rubber composition contains uncured rubber, and a rubber hardened product obtained by hardening the uncured rubber in the rubber composition is formed as a masterbatch, and then the masterbatch is molded together with an additional component to obtain a molded body; (3) A method in which the rubber component in the rubber composition is a thermoplastic elastomer, and the rubber composition alone or together with an additional component is melt-molded to obtain a molded body. Molding can be performed by injection molding, extrusion molding, extrusion profile molding, hollow molding, compression molding, etc.

In the method (2) above, the mass ratio of the masterbatch/additional components in the rubber hardener may be, for example, 1/99 to 99/1, or 5/95 to 95/5, or 10/90 to 90/10, or 20/80 to 80/20, or 30/70 to 70/30, or 40/60 to 60/40.

In one embodiment, the rubber cured product is a cured product of the rubber composite of the present invention. In one embodiment, the rubber cured product can be manufactured by a method comprising the following steps: obtaining a rubber composite by the method for manufacturing a rubber composite of the present invention; and curing the rubber composite to obtain the rubber cured product. In one embodiment, the rubber cured product can be obtained by vulcanization press according to JIS K6299.

The rubber hardened material can be formed into various shapes. The formed body can be used for a wide range of purposes, such as industrial mechanical parts, general mechanical parts, automobile/railway/vehicle/ship/aerospace related parts, electronic/electrical parts, construction/civil engineering materials, daily necessities, sports/entertainment products, wind power shell components, container/packaging components, etc. As examples of uses, the following molded products can be formed, such as automobile parts (for example, tires, bumpers, fenders, door inner panels, various moldings, logos, hoods, wheel covers, roofs, spoilers, various aerodynamic kits and other exterior parts; and dashboards, console boxes, accessories and other interior parts), battery parts (on-vehicle secondary battery parts, lithium-ion secondary battery parts, fuel tanks for solid methanol batteries, fuel cell piping, etc.), electronic/electrical machine parts (for example, various computers and their peripherals, junction boxes, various connectors, various OA machines, TVs, VCRs, CD players, bottom plates, refrigerators, air conditioners, liquid crystal projectors, etc.), daily necessities (shoe outsoles, etc.), etc.

One aspect of the present invention is to provide a shoe outsole, tire, anti-vibration rubber, or transmission belt comprising the rubber vulcanized material of the present invention. [Example]

Hereinafter, exemplary embodiments are given to further illustrate exemplary aspects of the present invention, but the present invention is not limited to these exemplary embodiments.

<Evaluation method><Liquidrubber> [Ethylene content, aromatic styrene content] The sample was dissolved in deuterated chloroform and measured using ¹³ C-NMR (ECZ500 from JEOL) under the following conditions. Resonance frequency: 125 MHz Pulse width: 90° Repetition time: 8 sec Accumulation: 5120 times Temperature: room temperature Chemical shift reference: CDCl ₃ 77.0 ppm

[Viscosity at 25°C] The viscosity of liquid rubber is measured using a B-type viscometer at 10 rpm.

[Number average molecular weight (Mn) and weight average molecular weight (Mw)] The chromatogram was measured using a GPC column connected with three columns filled with polystyrene gel. Standard polystyrene was used to calculate the molecular weight (Mn, Mw) and molecular weight distribution (Mw/Mn) by calibration curve. Tetrahydrofuran was used as solvent.

<Rubber composition> [Appearance (dispersibility of cellulose nanofibers)] The rubber compositions obtained in Examples 1 to 5 and Comparative Examples 2 and 3 were observed under an optical microscope under the following conditions. 1 mg of the sample was sandwiched between two cover glasses, crushed and spread to a uniform thickness. The sample was placed on the stage of a polarizing microscope BX51P manufactured by Olympus. A differential interference prism U-DICR manufactured by Olympus was inserted for differential interference observation. The dispersibility of the filler was evaluated based on the following criteria. A: Dispersed roughly uniformly. B: Although dispersed, aggregation was visible. C: Agglomeration was mostly confirmed.

[Storage modulus] For the rubber compositions of Examples 1 to 5, Comparative Examples 2 and 3, and the liquid rubber of Comparative Example 1, the storage modulus was measured using a rheometer HAAKE MARS40 manufactured by Thermo Fisher Scientific at 25°C, a strain of 0.002%, and a gap of 1 mm using parallel plates. A higher storage modulus indicates that the cellulose nanofibers are better dispersed in the rubber, which means that when the cellulose nanofibers are mixed into the rubber as a rubber masterbatch, the cellulose nanofibers are well dispersed in the rubber, and a rubber composition with excellent mechanical properties such as elastic modulus, storage modulus, and hardness can be obtained.

<Dry powder> For dry powder, the following evaluation was performed using a powder tester (model: PT-X) manufactured by Hosokawa Micron Co., Ltd.

[Loose density] Use a medicine spoon to add the dried substance at 10 g/min into a 100 mL stainless steel cylindrical container with a bottom (inner diameter 50.46 mm × depth 50 mm) until it overflows. Smooth the dried substance and measure the weight to 0.01 g. Divide the average of the three measured weights by the volume of the bottomed cylindrical container to calculate the loose density.

[Tapped density] A resin adapter (inner diameter 50.46 mm × length 40 mm) of sufficient capacity is connected to the top of the bottomed cylindrical container that is the same as the bottomed cylindrical container used in the loose density in a close-fitting manner. After adding the dry body until it overflows in the same procedure as the loose density measurement, a motor with an eccentric hammer installed on the rotating shaft is used to apply vibration with an amplitude of 1.5 mm and 50 Hz for 30 seconds to the bottomed cylindrical container in the state where the adapter is connected. Then, the adapter is removed, the dry body is smoothed, and the weight is measured to 0.01 g. The average value of the weight measured three times is divided by the content volume of the above bottomed cylindrical container to calculate the tapped density.

<Rubber cured product> The following evaluations were performed on the rubber cured product. (1) Tensile strength Evaluation was performed using the tensile test method of JIS K-6251. (2) Storage modulus The storage modulus at 50°C, 10 Hz frequency, and 3% strain was evaluated by torsion using the viscoelastic tester ARES-G2 manufactured by TA Instruments. (3) Dispersion of cellulose nanofibers The dispersion state of cellulose nanofibers was evaluated visually in a 5 cm square area on the vulcanization press surface of the rubber cured product using the following criteria. A: No agglomerates were visually confirmed B: A few (1 to 10) agglomerates were confirmed. C: Many agglomerates were confirmed (more than 11).

《Materials used》 ＜Liquid rubber＞ Liquid rubber-1: Butadiene-styrene random copolymer (RICON 184, available from Cray Valley), viscosity at 25°C 40,000 cP, number average molecular weight (Mn) 3,200, weight average molecular weight (Mw) 14,000, Mw/Mn 4.3, ethylene content 19 mol%, aromatic styrene content 8 mol% Liquid rubber-2: Butadiene-styrene random copolymer (RICON 100, available from Cray Valley), viscosity at 25°C 75,000 cP, number average molecular weight (Mn) 2,100, weight average molecular weight (Mw) 4,500, Mw/Mn 2.1, ethylene content 42 mol%, aromatic styrene content 9 mol%

<Solution polymerized rubber> Rubber-1: Asaprene Y031 (available from Asahi Chemical Co., Ltd.)

<Cellulose nanofiber> CNF-1: Micro-fibrous cellulose (Celish KY-100G, available from Daicel Miraizu Co., Ltd.)

CNF-2: Micro-fibrous cellulose 3 parts by mass of cotton linter pulp was soaked in 27 parts by mass of water and dispersed using a pulper. 170 parts by mass of water was added to 30 parts by mass of the cotton linter pulp treated by a pulper (including 3 parts by mass of cotton linter pulp) and dispersed in water (solid content 1.5% by mass). The SDR14 laboratory refiner (pressurized disk type) manufactured by Aikawa Iron Works Co., Ltd. was used as a disk refiner, and the gap between the disks was set to 1 mm. The water dispersion was pulped for 30 minutes. Then, the pulp was thoroughly beaten under the condition that the gap was reduced to a level close to zero, and a pulped water dispersion (solid content concentration: 1.5 mass%) was obtained. The obtained pulped water dispersion was directly subjected to 10 micronization treatments at an operating pressure of 100 MPa using a high-pressure homogenizer (NSO15H manufactured by Niro Soavi (Italy)) to obtain a micronized cellulose fiber slurry (solid content concentration: 1.5 mass%). Then, it was concentrated to a solid content rate of 10 mass% by a dehydrator to obtain a CNF-2 concentrated cake.

<Non-ionic surfactants> Surfactant-1: Polyoxyethylene (2) monolauryl ether (Emulgen102KG, available from Kao Corporation) () is the number of repetitions of ethylene oxide chains Surfactant-2: Sorbitan monooleate (HEODOL SP-O10V, available from Kao Corporation) Surfactant-3: Polyoxyethylene (6) sorbitan monolaurate (RHEODOL TW-L106, available from Kao Corporation) () is the number of repetitions of ethylene oxide chains Surfactant-4: Ethylene glycol-propylene glycol copolymer (PEG-PPG) (SANNIX GL-3000, available from Sanyo Chemical Co., Ltd.)

<Thermoplastic elastomer> SEBS H1052: Product name "Tuftec H1052", manufactured by Asahi Kasei Co., Ltd.

<Silicon dioxide> Silicon dioxide-1: precipitated silicon dioxide (ULTRASIL 7000GR, available from Degussa)

<Silane coupling agent> Si75: Bis(3-(triethoxysilyl)propyl) disulfide (available from Evonik Japan)

＜Oil＞ PF30: Mineral oil (available from JXTG Energy Co., Ltd.)

<Vulcanization aid> Zinc oxide: Available from FUJIFILM Wako Chemicals (Co., Ltd.) Stearic acid: Available from FUJIFILM Wako Chemicals (Co., Ltd.)

＜Wax＞ Selective special wax: Selected special wax (available from Da Nei Shinko Chemical Co., Ltd.)

＜Anti-aging agent＞ Nocrack 6C: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (available from Da Nei Shinko Chemical Co., Ltd.)

<Vulcanization accelerator> Nocceler CZ: N-cyclohexyl-2-benzothiazolylsulfenamide (available from Da Nei Shinko Chemical Co., Ltd.) Nocceler D: 1,3-diphenylguanidine (available from Da Nei Shinko Chemical Co., Ltd.)

《Preparation of rubber composition》 ＜Example 1＞ Add purified water to Celish KY100G (manufactured by Daicel FineChem) (aqueous dispersion of cellulose fibers) to prepare an aqueous dispersion having a final cellulose nanofiber content of 5% by mass. Add liquid rubber-1 (RICON184) and surfactant-1 thereto to prepare an aqueous dispersion having a final composition of 90% by mass of water, 5% by mass of cellulose fibers, 2.86% by mass of liquid rubber, and 2.14% by mass of surfactant. Use an ARE-310 rotary-revolution stirrer manufactured by Thinky Co., Ltd. to mix the aqueous dispersion for 5 minutes to obtain a dispersion of a cellulose nanofiber composition. The obtained dispersion was dried at 80°C using SPH-201 manufactured by ESPEC Co., Ltd. to obtain a dried body. The obtained dried body was crushed using Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd., and 20 parts by mass of the dried body was added to 80 parts by mass of liquid rubber-1 (RICON184), and mixed for 15 minutes using an auto-revolution mixer ARE-310 manufactured by Thinky Co., Ltd. to obtain a rubber composition.

<Example 2> Purified water was added to Celish KY100G (manufactured by Daicel FineChem) (aqueous dispersion of cellulose fibers) to prepare an aqueous dispersion having a final cellulose nanofiber content of 5% by mass. Surfactant-1 was added thereto to prepare an aqueous dispersion having a final composition of 92.86% by mass of water, 5% by mass of cellulose fibers, and 2.14% by mass of surfactant. The aqueous dispersion was mixed for 5 minutes using an ARE-310 rotary-revolution stirrer manufactured by Thinky Co., Ltd. to obtain a dispersion of a cellulose nanofiber composition. The obtained dispersion was dried at 80°C using SPH-201 manufactured by ESPEC Co., Ltd. to obtain a dried body. The obtained dried body was crushed using Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd., and 14.29 parts by mass of the dried body was added to 85.71 parts by mass of liquid rubber-1 (RICON 184), and mixed for 15 minutes using an ARE-310 rotary mixer manufactured by Thinky Co., Ltd. to obtain a rubber composition.

<Example 3> Except that surfactant-2 was used instead of surfactant-1, a rubber composition was prepared under the same conditions as in Example 2.

<Example 4> Except that surfactant-3 was used instead of surfactant-1, a rubber composition was prepared under the same conditions as in Example 2.

<Example 5> Except that surfactant-4 was used instead of surfactant-1, a rubber composition was prepared under the same conditions as in Example 2.

<Comparison Example 1> Liquid Rubber-1 (RICON184) was used directly.

<Comparative Example 2> 10 parts by mass of silica-1 were added to 90 parts by mass of liquid rubber-1 (RICON 184), and mixed for 15 minutes using an ARE-310 rotary mixer manufactured by Thinky Co., Ltd. to obtain a rubber composition.

<Comparative Example 3> Purified water was added to Celish KY100G (manufactured by Daicel FineChem) (aqueous dispersion of cellulose fibers) to prepare an aqueous dispersion having a final cellulose nanofiber content of 5% by mass. Liquid rubber-1 (RICON184) was added thereto to obtain an aqueous dispersion having a final composition of 92.86% by mass of water, 5% by mass of cellulose fibers, and 2.14% by mass of liquid rubber-1. The aqueous dispersion was mixed for 5 minutes using an ARE-310 rotary-revolution stirrer manufactured by Thinky Co., Ltd. to obtain a dispersion of a cellulose nanofiber composition. The obtained dispersion was dried at 80°C using SPH-201 manufactured by ESPEC Co., Ltd. to obtain a dried body. The obtained dried body was crushed using Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd., and 14.29 parts by mass of the crushed dried body was added to 85.71 parts by mass of liquid rubber-1 (RICON 184), and mixed for 15 minutes using an ARE-310 rotary mixer manufactured by Thinky Co., Ltd. to obtain a rubber composition.

The results are shown in Table 1. In Examples 1 to 5, the cellulose nanofibers were well dispersed in the rubber, and the storage modulus at a frequency of 1 Hz was high. In Comparative Example 3, many agglomerates were contained in the rubber, and although the storage modulus was measured, a stable measured value was not obtained.

[Table 1] Table 1 Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Comparison Example 1 Comparison Example 2 Comparison Example 3 Rubber composition (mass %) Liquid Rubber-1 85.71 85.71 85.71 85.71 85.71 100 90 90 CNF-1 10 10 10 10 10 10 Surfactant-1 4.29 4.29 Surfactant-2 4.29 Surfactant-3 4.29 Surfactant-4 4.29 Silica-1 10 Reviews Storage modulus at 1 Hz frequency (Pa) 34393 18025 22767 18575 10706 12 360 Unable to determine Filler dispersion (A～C) A A A A A -- A C

<Dispersion of rubber composition in thermoplastic elastomer> <Example 6> Purified water was added to Celish KY100G (manufactured by Daicel FineChem) (aqueous dispersion of cellulose fibers) to prepare an aqueous dispersion having a final cellulose nanofiber content of 5% by mass. Liquid rubber-2 (RICON100) and surfactant-1 were added thereto to prepare an aqueous dispersion having a final composition of 90% by mass of water, 5% by mass of cellulose fibers, 7.86% by mass of liquid rubber, and 2.14% by mass of surfactant. The aqueous dispersion was mixed for 15 minutes using an ARE-310 rotary-revolution stirrer manufactured by Thinky Co., Ltd. to obtain a dispersion of the cellulose nanofiber composition. Using SPH-201 manufactured by ESPEC Co., Ltd., the obtained dispersion was dried at 80°C to obtain a rubber composition.

Then, using a small mixer (Xplore) manufactured by Rheolabo, 15 g of the rubber composition was added to 85 g of thermoplastic elastomer-1 (SEBS H1052), and melt-kneaded at 200°C for 5 minutes to obtain a rubber strand in which cellulose nanofibers were dispersed. The obtained rubber strand was hot-pressed at 200°C and 10 kN for 10 minutes to obtain a sheet. The sheet was visually observed, and no agglomerates were observed.

<Comparative Example 4> Purified water was added to Celish KY100G (manufactured by Daicel FineChem) (aqueous dispersion of cellulose fibers) to prepare an aqueous dispersion having a final cellulose nanofiber content of 5% by mass. Surfactant-1 was added thereto to prepare an aqueous dispersion having a final composition of 92.86% by mass of water, 5% by mass of cellulose fibers, and 2.14% by mass of surfactant. The aqueous dispersion was mixed for 15 minutes using an ARE-310 rotary-revolution stirrer manufactured by Thinky Co., Ltd. to obtain a dispersion of a cellulose nanofiber composition. Using SPH-201 manufactured by ESPEC Co., Ltd., the obtained dispersion was dried at 80°C to obtain a composition containing cellulose nanofibers.

Then, using a small mixer (Xplore) manufactured by Rheolabo, 7.1 g of the composition containing cellulose nanofibers was added to 92.9 g of thermoplastic elastomer-1 (SEBS H1052), and melt-kneaded at 200°C for 5 minutes to obtain a rubber strand in which cellulose nanofibers were dispersed. The obtained rubber strand was hot-pressed at 200°C and 10 kN for 10 minutes to obtain a sheet. The sheet was visually observed, and many agglomerates were confirmed.

<Manufacturing of rubber cured product> <Example 7> Purified water was added to CNF-2 (aqueous dispersion of cellulose fibers) to prepare an aqueous dispersion having a final cellulose nanofiber content of 5% by mass. Liquid rubber-1 and surfactant-1 were added thereto to prepare an aqueous dispersion having a final composition of 90% by mass of water, 5% by mass of cellulose fibers, 2.86% by mass of liquid rubber, and 2.14% by mass of surfactant. The aqueous dispersion was mixed for 5 minutes using an ARE-310 rotary-revolution stirrer manufactured by Thinky Co., Ltd. to obtain a dispersion of a cellulose nanofiber composition. The obtained dispersion was dried at 80°C using SPH-201 manufactured by ESPEC Co., Ltd. to obtain a dry body. The obtained dry body was crushed for 30 seconds using Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd. to obtain a powder for the production of rubber cured products. The loose density and tap density of the obtained dry powder were measured using the above method.

Next, the Labo Plastomill manufactured by Toyo Seiki Co., Ltd. was heated to 70°C, 100 parts by mass of rubber-1 (Asaprene Y031) was added and kneaded for 0.5 minutes, 10 parts by mass of powder for producing a rubber hardener, a vulcanizing aid (2.5 parts by mass of zinc white and 2 parts by mass of stearic acid), 1.5 parts by mass of wax, and 2 parts by mass of an antioxidant were added thereto and kneaded for 5.5 minutes, and a primary kneading was performed. Next, the primary kneading composition obtained was added to the Labo Plastomill heated to 70°C and kneaded for 0.5 minutes, and 1.7 parts by mass of sulfur and a vulcanization accelerator (1.7 parts by mass of Nocceler CZ and 2 parts by mass of Nocceler D) were added thereto according to the composition shown in Table 2 and kneaded for 2 minutes. The obtained secondary kneaded composition was vulcanized by vulcanization pressing at 160° C. for 20 minutes to obtain a rubber cured product.

<Example 8> The rubber hardened material was obtained in the same manner as in Example 7 except that a hammer mill made by Fredrive of Frewitt Company was used instead of Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd. to crush the dried body.

<Example 9> The rubber hardened material was obtained in the same manner as in Example 7 except that the cone screen mill of Fredrive manufactured by Frewitt was used instead of the Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd. to pulverize the dried body.

<Example 10> The rubber hardened material was obtained in the same manner as in Example 7 except that a pin mill made by Fredrive of Frewitt Company was used instead of Mini Speed Mill MS-05 made by Labonect Co., Ltd. to grind the dried body.

The powder obtained by crushing the dried body was dyed with OsO ₄ for 12 hours, mixed with epoxy resin, and left at room temperature for 48 hours to harden the epoxy resin. The hardened sample was cut by ultra-thin slicer to make a smooth cross section, and Os plasma coating was performed for 1 second. The sample was observed by scanning electron microscope (Hitachi High-Technologies Corporation, SU8220) under the conditions of accelerating voltage 1.5 kV, WD 3 mm, and upper detector. The result showed that the cellulose nanofibers were covered by the rubber component (Figure 1). In Figure 1, the dark gray part is the cellulose nanofiber, the thin gray part around the cellulose nanofiber is the first rubber component, and the black part is the epoxy resin. According to FIG. 1 , it was confirmed that the cellulose nanofibers were covered with the first rubber component.

<Example 11> Except that surfactant-2 is used instead of surfactant-1 as the surfactant, a rubber cured product is obtained in the same manner as in Example 7.

<Example 12> An aqueous dispersion was prepared in a manner of 92.86 mass % of water, 5 mass % of cellulose fiber, 1.43 mass % of liquid rubber, and 0.71 mass % of surfactant, instead of 90 mass % of water, 5 mass % of cellulose fiber, 2.86 mass % of liquid rubber, and 2.14 mass % of surfactant as the final composition when preparing the aqueous dispersion, and 7.14 mass parts of powder for producing a rubber cured product were added during the first kneading instead of 10 mass parts of powder for producing a rubber cured product. A rubber cured product was obtained in the same manner as in Example 7, except that.

<Example 13> An aqueous dispersion was prepared in a manner of 93.58 mass % of water, 5 mass % of cellulose fiber, 0.71 mass % of liquid rubber, and 0.71 mass % of surfactant, instead of 90 mass % of water, 5 mass % of cellulose fiber, 2.86 mass % of liquid rubber, and 2.14 mass % of surfactant as the final composition when preparing the aqueous dispersion, and 6.42 mass parts of powder for producing a rubber cured product were added during the first kneading instead of adding 10 mass parts of powder for producing a rubber cured product. A rubber cured product was obtained in the same manner as in Example 7, except that.

<Example 14> An aqueous dispersion was prepared in a manner of 85% water, 5% cellulose fiber, 7.86% liquid rubber, and 2.14% surfactant, instead of 90% water, 5% cellulose fiber, 2.86% liquid rubber, and 2.14% surfactant as the final composition when preparing the aqueous dispersion, and a Freezer mill 6875 manufactured by SPEX was used instead of the Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd., and the dried body was pulverized by freeze pulverization. A rubber cured product was obtained in the same manner as in Example 7.

<Example 15> The Labo Plastomill manufactured by Toyo Seiki Co., Ltd. was heated to 70°C, 100 parts by mass of rubber-1 (Asaprene Y031) was added and kneaded for 0.5 minutes, 30 parts by mass of the powder for producing the rubber hardener produced in Example 7 was added thereto, and kneaded for 5.5 minutes to prepare a masterbatch. Thereafter, the Labo Plastomill was heated to 70°C, 67 parts by mass of rubber-1 (Asaprene Y031) and 43 parts by mass of the masterbatch were added and kneaded for 0.5 minutes, a vulcanizing aid (2.5 parts by mass of zinc white and 2 parts by mass of stearic acid), 1.5 parts by mass of wax, and 2 parts by mass of an antioxidant were added and kneaded for 5.5 minutes, and kneading was performed once. Then, 1.7 parts by mass of sulfur and a vulcanization accelerator (1.7 parts by mass of Nocceler CZ and 2 parts by mass of Nocceler D) were added and kneaded for 2 minutes. The obtained secondary kneaded composition was vulcanized at 160°C for 20 minutes using a vulcanization press to obtain a rubber hardened material.

<Reference Example 5> The dried body was dried by reduced pressure drying at 80°C using a Henschel mixer instead of using SPH-201 manufactured by ESPEC Co., Ltd. for drying at 80°C, and the dried powder was not crushed for use. A rubber cured product was obtained in the same manner as in Example 7.

<Reference Example 6> Except that the grinding time of the dried body was changed from 30 seconds to 5 seconds, the rubber hardened material was obtained in the same manner as in Example 7.

<Reference Example 7> Purified water was added to CNF-2 (aqueous dispersion of cellulose fibers) to prepare an aqueous dispersion having a final cellulose nanofiber content of 5% by mass. Liquid rubber-1 and surfactant-1 were added thereto to prepare an aqueous dispersion having a final composition of 82.86% by mass of water, 5% by mass of cellulose fibers, 10% by mass of liquid rubber, and 2.14% by mass of surfactant. The aqueous dispersion was mixed for 5 minutes using an ARE-310 rotary-revolution stirrer manufactured by Thinky Co., Ltd. to obtain a dispersion of a cellulose nanofiber composition. The obtained dispersion was dried at 80°C using SPH-201 manufactured by ESPEC Co., Ltd. to obtain a dried product. The obtained dried body was processed for 30 seconds using Mini Speed Mill MS-05 manufactured by Labonect Co., Ltd. The dried body after processing did not become powder but fragments of several mm in size.

Next, the Labo Plastomill manufactured by Toyo Seiki Co., Ltd. was heated to 70°C, 100 parts by mass of rubber-1 (Asaprene Y031) was added and kneaded for 0.5 minutes, 17.14 parts by mass of powder for producing a rubber hardened material, a vulcanizing aid (2.5 parts by mass of zinc white and 2 parts by mass of stearic acid), 1.5 parts by mass of wax, and 2 parts by mass of an antioxidant were added thereto and kneaded for 5.5 minutes, and a primary kneading was performed. Next, the obtained primary kneading composition was added to the Labo Plastomill heated to 70°C and kneaded for 0.5 minutes, and 1.7 parts by mass of sulfur and a vulcanization accelerator (1.7 parts by mass of Nocceler CZ and 2 parts by mass of Nocceler D) were added thereto according to the composition shown in Table 2 and kneaded for 2 minutes. The obtained secondary kneaded composition was vulcanized at 160°C for 20 minutes by vulcanization pressing to obtain a rubber cured product.

<Evaluation results of Examples 7 to 15 and Reference Examples 5 to 7> Table 2 shows the evaluation results of Examples 7 to 15 and Reference Examples 5 to 7. It was confirmed that the cellulose nanofibers were well dispersed in the rubber in the examples and the physical properties were significantly improved.

[Table 2] Table 2 Unit Embodiment 7 Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 Embodiment 12 Embodiment 13 Embodiment 14 Embodiment 15 Reference Example 5 Reference Example 6 Reference Example 7 Rubber composition dispersion composition water Quality% 90.00 90.00 90.00 90.00 90.00 92.86 93.58 85.00 Same as Example 7 90.00 90.00 82.86 Fiber CNF-2 Quality% 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 Non-ionic surfactant Surfactant-1 Quality% 2.14 2.14 2.14 2.14 0.71 0.71 2.14 2.14 2.14 2.14 Surfactant-2 Quality% 2.14 Liquid Rubber Liquid Rubber-1 Quality% 2.86 2.86 2.86 2.86 2.86 1.43 0.71 7.86 2.86 2.86 10.00 Reviews Powder Loose packing density g/cm ³ 0.095 0.089 0.196 0.073 0.138 0.127 0.234 0.096 0.360 0.315 Not powdered Tap density g/cm ³ 0.200 0.138 0.387 0.101 0.188 0.237 0.308 0.210 0.591 0.465 Rubber hardener Storage module MPa 1.51 1.68 1.45 1.71 1.47 1.44 1.31 2.10 1.66 0.84 0.92 0.79 Tensile strength MPa 2.04 2.61 1.96 2.77 2.11 2.15 1.78 3.51 2.39 1.60 1.53 1.21 Dispersibility (visual) A～C A A B A A A B A A C C C [Industrial Availability]

The rubber composition of the present invention can be formed into a molded body with good physical properties, and is therefore suitable for a wide range of uses, such as industrial mechanical parts, general mechanical parts, automobile/railway/vehicle/ship/aerospace related parts, electronic/electrical parts, building/civil engineering materials, daily necessities, sports/entertainment products, wind power shell components, container/packaging components, etc.

FIG. 1 is a diagram showing an observation image of a cross section of the powder obtained in Example 10 obtained by a scanning electron microscope.

Claims (27)

A rubber composition comprising cellulose nanofibers, a first rubber component of a liquid rubber, and a non-ionic surfactant, wherein the degree of substitution of the cellulose nanofibers is 0. As in claim 1, the rubber composition, wherein the cellulose nanofibers do not have ionic groups. The rubber composition of claim 1 or 2, wherein the number average molecular weight of the liquid rubber is 1,000~80,000. The rubber composition of claim 1 or 2, wherein the ratio (Mw/Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) of the liquid rubber is 1.5 to 5. The rubber composition of claim 1 or 2, wherein the viscosity of the liquid rubber at 80°C is less than 1,000,000 mPa‧s. The rubber composition of claim 1 or 2, wherein the viscosity of the liquid rubber at 25°C is less than 1,000,000 mPa‧s. The rubber composition of claim 1 or 2, wherein the viscosity of the liquid rubber at 0°C is less than 1,000,000 mPa‧s. The rubber composition of claim 1 or 2, wherein the liquid rubber comprises one or more selected from the group consisting of diene rubber, silicone rubber, urethane rubber, polysulfide rubber and hydrogenated products thereof. The rubber composition of claim 1 or 2 contains 0.5% to 10% by mass of the above-mentioned cellulose nanofibers. The rubber composition of claim 1 or 2 comprises 10 to 200 parts by mass of the above-mentioned non-ionic surfactant relative to 100 parts by mass of the above-mentioned cellulose nanofibers. As in claim 1 or 2, the rubber composition, wherein the non-ionic surfactant is a compound having a hydrophilic group and a hydrocarbon group, and the hydrophilic group is selected from the group consisting of a hydroxyl group, a carboxyl group, a sulfonic acid group, and an amino group. The rubber composition of claim 11, wherein the nonionic surfactant is selected from a compound represented by the following general formula (1): R-(OCH ₂ CH ₂ ) _m -OH (1) [wherein R represents a monovalent aliphatic group having 6 to 30 carbon atoms, and m is a natural number less than the carbon number of R], and the following general formula (2): R ₁ OCH ₂ -(CHOH) ₄ -CH ₂ OR ₂ (2) [wherein R ₁ and R ₂ independently represent a hydrogen atom, an aliphatic group having 1 to 30 carbon atoms, - COR ₃ {wherein R ₃ represents an aliphatic group having 1 to 30 carbon atoms}, or -(CH ₂ CH ₂ O) _y -R ₄ {wherein R ₄ represents a hydrogen atom or an aliphatic group having 1 to 30 carbon atoms, and y is an integer of 1 to 30}] at least one of the group consisting of the compounds represented by. A rubber composition as claimed in any one of claim 1 or 2, wherein at least a portion of the surface of the cellulose nanofiber is covered by the first rubber component. A powder composed of a rubber composition as described in any one of claims 1 to 13. For example, the powder of claim 14 has a tap density of 0.01 g/cm ³ to 0.30 g/cm ³ . A masterbatch, which is a mixture of the powder as in claim 14 or 15 and the second rubber component. A method for producing a masterbatch, comprising the following steps: mixing the powder as in claim 14 or 15 with the second rubber component to obtain a masterbatch. A rubber compound, which is a mixture of the powder of claim 14 or 15 or the masterbatch of claim 16 and a third rubber component. A rubber composite as claimed in claim 18, wherein at least a portion of the surface of the cellulose nanofiber is covered by the first rubber component. A method for manufacturing a rubber composite, comprising the following steps: kneading the powder as in claim 14 or 15 with a third rubber component, or forming a masterbatch using the method as in claim 17, and then kneading the masterbatch with the third rubber component to obtain a rubber composite. As in the method of claim 20, wherein in the rubber composite, at least a portion of the surface of the cellulose nanofiber is coated by the first rubber component. A rubber hardener, which is a hardener of the rubber composite of claim 18 or 19. A method for manufacturing a rubber hardener, comprising: a step of obtaining a rubber composite using the method of claim 20 or 21; and a step of hardening the rubber composite to obtain a rubber hardener. A shoe outsole comprising a rubber vulcanized material as claimed in claim 22. A tire comprising a rubber vulcanizer as claimed in claim 22. A vibration-resistant rubber comprising a rubber hardener as described in claim 22. A transmission belt comprising a rubber vulcanized material as claimed in claim 22.